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>

docs/options.md

@@ -22,6 +22,17 @@ Valid options:
 | ------- | -------------------------- | ------------------------------- |
 | `false` | `--experimental-ternaries` | `experimentalTernaries: <bool>` |
 
+## Experimental Operator Position
+
+Valid options:
+
+- `"start"` - When binary expressions wrap lines, print operators at the start of new lines.
+- `"end"` - Default behavior; when binary expressions wrap lines, print operators at the end of previous lines.
+
+| Default | CLI Override                                                   | API Override                                                  |
+| ------- | -------------------------------------------------------------- | ------------------------------------------------------------- |
+| `"end"` | <code>--experimental-operator-position <start&#124;end></code> | <code>experimentalOperatorPosition: "<start&#124;end>"</code> |
+
 ## Print Width
 
 Specify the line length that the printer will wrap on.