[llvm] [YAMLParser] Improve plain scalar spec compliance (PR #68946)

[via llvm-commits]

================
@@ -392,6 +392,10 @@ class Scanner {
   ///        Pos is whitespace or a new line
   bool isBlankOrBreak(StringRef::iterator Position);
 
+  /// Return true if the minimal well-formed code unit subsequence at
+  ///        Pos is considered a "safe" character for plain scalars.
----------------
akirchhoff-modular wrote:

The declaration immediately before this also seems to have this unusual spacing:

```cpp
  /// Return true if the minimal well-formed code unit subsequence at
  ///        Pos is whitespace or a new line
  bool isBlankOrBreak(StringRef::iterator Position);
```

I also thought this was unusual, but I figured it would be better to be consistent with the existing code. That said, I am happy to change this if you still think it makes sense.

https://github.com/llvm/llvm-project/pull/68946