Break lines before binary operators (#7111)

* Add additional binary expression comment tests

Refs #3806

These cover a few edge cases I encountered while maintaining
`@btmills/prettier` over the last few years. I'm adding them up front to
demonstrate that the `experimentalOperatorPosition` changes in a later
commit have no effect on this formatting when the flag is not enabled.

* Define experimentalOperatorPosition flag

Refs #3806

This merely defines the flag. A future commit will use it in updated
logic.

* Add experimentalOperatorPosition default tests

Right now, this flag isn't implemented, so these tests duplicate the
existing behavior. I'm adding them now so that when I implement the
flag's logic in a future commit, the changed formatting will be obvious
in the diff and easier to review.

* Implement experimentalOperatorPosition flag

Fixes #3806 as requested in https://github.com/prettier/prettier/pull/7111#issuecomment-2252623779

The flag's tests were already added in a previous commit, so the test
changes you see in this commit are specifically due to the new flag's
implementation.

* Document experimentalOperatorPosition flag

* Change operator position option start|end

In response to https://github.com/prettier/prettier/pull/7111#discussion_r1729382119

* Add TS intersection line wrapping tests

This clones TypeScript's type union operator tests in `union-parens.ts`
and swaps the operators (& <-> |) to test the the type interesection
operator. It also runs intersection tests with the new
`experimentalOperatorPosition: "start"` flag. This does _not_ yet update
the implementation to consider the flag; to ease review, I'll make that
change in the next commit to isolate the impact of the change.

* Apply experimentalOperatorPosition: start to type intersections

The type union operator was already formatted at the beginning of lines
by default, so that logic didn't need to be updated.

* Update 7111.md

* Update tests after rebasing

I rebased from 1dfe28f85 to c7066780e to fix test failures related to
https://github.com/prettier/prettier/pull/16601. The rebase applied
cleanly, and this was the only change to tests. Since the PR has
already been approved, I'll keep this as a separate commit rather than
squashing into the prior commits.

---------

Co-authored-by: fisker Cheung <lionkay@gmail.com>
Co-authored-by: SUZUKI Sosuke <aosukeke@gmail.com>

tests/integration/__tests__/__snapshots__/early-exit.js.snap

@@ -53,6 +53,9 @@ Format options:
   --end-of-line <lf|crlf|cr|auto>
                            Which end of line characters to apply.
                            Defaults to lf.
+  --experimental-operator-position <start|end>
+                           Where to print operators when binary expressions wrap lines.
+                           Defaults to end.
   --no-experimental-ternaries
                            Default behavior of ternaries; keep question marks on the same line as the consequent.
   --html-whitespace-sensitivity <css|strict|ignore>
@@ -218,6 +221,9 @@ Format options:
   --end-of-line <lf|crlf|cr|auto>
                            Which end of line characters to apply.
                            Defaults to lf.
+  --experimental-operator-position <start|end>
+                           Where to print operators when binary expressions wrap lines.
+                           Defaults to end.
   --no-experimental-ternaries
                            Default behavior of ternaries; keep question marks on the same line as the consequent.
   --html-whitespace-sensitivity <css|strict|ignore>

tests/integration/__tests__/__snapshots__/help-options.js.snap

@@ -191,6 +191,23 @@ Default: lf"
 
 exports[`show detailed usage with --help end-of-line (write) 1`] = `[]`;
 
+exports[`show detailed usage with --help experimental-operator-position (stderr) 1`] = `""`;
+
+exports[`show detailed usage with --help experimental-operator-position (stdout) 1`] = `
+"--experimental-operator-position <start|end>
+
+  Where to print operators when binary expressions wrap lines.
+
+Valid options:
+
+  start   Print operators at the start of new lines.
+  end     Print operators at the end of previous lines.
+
+Default: end"
+`;
+
+exports[`show detailed usage with --help experimental-operator-position (write) 1`] = `[]`;
+
 exports[`show detailed usage with --help experimental-ternaries (stderr) 1`] = `""`;
 
 exports[`show detailed usage with --help experimental-ternaries (stdout) 1`] = `

tests/integration/__tests__/__snapshots__/plugin-options-string.js.snap

@@ -17,10 +17,10 @@ exports[`show external options with \`--help\` 1`] = `
 - First value
 + Second value
 
-@@ -24,16 +24,18 @@
-    --end-of-line <lf|crlf|cr|auto>
-                             Which end of line characters to apply.
-                             Defaults to lf.
+@@ -27,16 +27,18 @@
+    --experimental-operator-position <start|end>
+                             Where to print operators when binary expressions wrap lines.
+                             Defaults to end.
     --no-experimental-ternaries
                              Default behavior of ternaries; keep question marks on the same line as the consequent.
 +   --foo-string <string>    foo description

tests/integration/__tests__/__snapshots__/plugin-options.js.snap

@@ -60,10 +60,10 @@ exports[`show external options with \`--help\` 1`] = `
 - First value
 + Second value
 
-@@ -24,16 +24,18 @@
-    --end-of-line <lf|crlf|cr|auto>
-                             Which end of line characters to apply.
-                             Defaults to lf.
+@@ -27,16 +27,18 @@
+    --experimental-operator-position <start|end>
+                             Where to print operators when binary expressions wrap lines.
+                             Defaults to end.
     --no-experimental-ternaries
                              Default behavior of ternaries; keep question marks on the same line as the consequent.
 +   --foo-option <bar|baz>   foo description

tests/integration/__tests__/__snapshots__/schema.js.snap

@@ -89,6 +89,24 @@ exports[`schema 1`] = `
             },
           ],
         },
+        "experimentalOperatorPosition": {
+          "default": "end",
+          "description": "Where to print operators when binary expressions wrap lines.",
+          "oneOf": [
+            {
+              "description": "Print operators at the start of new lines.",
+              "enum": [
+                "start",
+              ],
+            },
+            {
+              "description": "Print operators at the end of previous lines.",
+              "enum": [
+                "end",
+              ],
+            },
+          ],
+        },
         "experimentalTernaries": {
           "default": false,
           "description": "Use curious ternaries, with the question mark after the condition.",

tests/integration/__tests__/__snapshots__/support-info.js.snap

@@ -130,6 +130,14 @@ exports[`API getSupportInfo() 1`] = `
       "default": "lf",
       "type": "choice",
     },
+    "experimentalOperatorPosition": {
+      "choices": [
+        "start",
+        "end",
+      ],
+      "default": "end",
+      "type": "choice",
+    },
     "experimentalTernaries": {
       "default": false,
       "type": "boolean",
@@ -847,6 +855,24 @@ exports[`CLI --support-info (stdout) 1`] = `
       "pluginDefaults": {},
       "type": "choice"
     },
+    {
+      "category": "JavaScript",
+      "choices": [
+        {
+          "description": "Print operators at the start of new lines.",
+          "value": "start"
+        },
+        {
+          "description": "Print operators at the end of previous lines.",
+          "value": "end"
+        }
+      ],
+      "default": "end",
+      "description": "Where to print operators when binary expressions wrap lines.",
+      "name": "experimentalOperatorPosition",
+      "pluginDefaults": {},
+      "type": "choice"
+    },
     {
       "category": "JavaScript",
       "default": false,