[clang] [clang-format] Introduce "ReflowComments: IndentOnly" to re-indent comments without breaking internal structure (think Doxygen). (PR #96804)

[Owen Pan via cfe-commits]

================
@@ -420,8 +420,10 @@ BreakableComment::getSplit(unsigned LineIndex, unsigned TailOffset,
                            unsigned ColumnLimit, unsigned ContentStartColumn,
                            const llvm::Regex &CommentPragmasRegex) const {
   // Don't break lines matching the comment pragmas regex.
-  if (CommentPragmasRegex.match(Content[LineIndex]))
+  if (Style.ReflowComments != FormatStyle::RCS_Always ||
----------------
owenca wrote:

```suggestion
  if (!AlwaysReflow ||
```
after adding the following to `BreakableToken.h`:
```c++
@@ -393,6 +393,8 @@ protected:
   // and not:
   // // comment 1comment 2
   StringRef ReflowPrefix = " ";
+
+  const bool AlwaysReflow = Style.ReflowComments == FormatStyle::RCS_Always;
 };
 
 class BreakableBlockComment : public BreakableComment {
```

https://github.com/llvm/llvm-project/pull/96804