Improve > handling in blockquote in Markdown (#19802)

Co-authored-by: codex <codex@openai.com>
Co-authored-by: fisker Cheung <lionkay@gmail.com>
Co-authored-by: fisker <lionkay@gmail.com>

tests/format/markdown/blockquote/prose-wrap-always/__snapshots__/format.test.js.snap

@@ -0,0 +1,162 @@
+// Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
+
+exports[`encoded-greater-than.md - {"proseWrap":"always"} format 1`] = `
+====================================options=====================================
+parsers: ["markdown"]
+proseWrap: "always"
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+> > a
+> > b
+
+> > a
+> > b
+
+> > a
+> > b
+
+> > a
+> > b
+
+> > a
+> > b
+
+> > a
+> > b
+
+=====================================output=====================================
+> > a > b
+
+> > a > b
+
+> > a > b
+
+> > a > b
+
+> > a > b
+
+> > a > b
+
+================================================================================
+`;
+
+exports[`encoded-newline.md - {"proseWrap":"always"} format 1`] = `
+====================================options=====================================
+parsers: ["markdown"]
+proseWrap: "always"
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+> a 
 b
+> > c
+
+> a 
 b
+> > c
+
+> a 
 b
+> \\> c
+
+> a 
 b
+    > c
+
+> a &newline; b
+> \\> c
+
+> a \\
 b
+> \\> c
+
+> a \\\\
 b
+> \\> c
+
+=====================================output=====================================
+> a 
 b > c
+
+> a 
 b > c
+
+> a 
 b \\> c
+
+> a 
 b > c
+
+> a &newline; b \\> c
+
+> a \\
 b \\> c
+
+> a \\\\
 b \\> c
+
+================================================================================
+`;
+
+exports[`escaped-greater-than.md - {"proseWrap":"always"} format 1`] = `
+====================================options=====================================
+parsers: ["markdown"]
+proseWrap: "always"
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+> \\>
+> \\>
+
+> *text* > \\>
+
+> abc
+> \\> abc
+
+=====================================output=====================================
+> \\> \\>
+
+> _text_ > \\>
+
+> abc \\> abc
+
+================================================================================
+`;
+
+exports[`indented-greater-than.md - {"proseWrap":"always"} format 1`] = `
+====================================options=====================================
+parsers: ["markdown"]
+proseWrap: "always"
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+> first
+    > second
+
+> first
+	> second
+
+> > first
+    > second
+
+> first
+    >> second
+
+=====================================output=====================================
+> first > second
+
+> first > second
+
+> > first > second
+
+> first >> second
+
+================================================================================
+`;
+
+exports[`issue-19528.md - {"proseWrap":"always"} format 1`] = `
+====================================options=====================================
+parsers: ["markdown"]
+proseWrap: "always"
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+> test\\>
+
+> **test**\\>
+
+> \\>
+
+=====================================output=====================================
+> test\\>
+
+> **test**\\>
+
+> \\>
+
+================================================================================
+`;

tests/format/markdown/blockquote/prose-wrap-always/encoded-greater-than.md

@@ -0,0 +1,17 @@
+> > a
+> > b
+
+> > a
+> > b
+
+> > a
+> > b
+
+> > a
+> > b
+
+> > a
+> > b
+
+> > a
+> > b

tests/format/markdown/blockquote/prose-wrap-always/encoded-newline.md

@@ -0,0 +1,20 @@
+> a 
 b
+> > c
+
+> a 
 b
+> > c
+
+> a 
 b
+> \> c
+
+> a 
 b
+    > c
+
+> a &newline; b
+> \> c
+
+> a \
 b
+> \> c
+
+> a \\
 b
+> \> c

tests/format/markdown/blockquote/prose-wrap-always/escaped-greater-than.md

@@ -0,0 +1,7 @@
+> \>
+> \>
+
+> *text* > \>
+
+> abc
+> \> abc

tests/format/markdown/blockquote/prose-wrap-always/format.test.js

@@ -0,0 +1 @@
+runFormatTest(import.meta, ["markdown"], { proseWrap: "always" });

tests/format/markdown/blockquote/prose-wrap-always/indented-greater-than.md

@@ -0,0 +1,11 @@
+> first
+    > second
+
+> first
+	> second
+
+> > first
+    > second
+
+> first
+    >> second

tests/format/markdown/blockquote/prose-wrap-always/issue-19528.md

@@ -0,0 +1,5 @@
+> test\>
+
+> **test**\>
+
+> \>