[clang] [AST] Iterate redecls starting from the canonical one in getRawCommentsForAnyRedecl() (PR #108475)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@HighCommander4 
I extended your test case a little to validate the `TemplateDeclKind` we would have.
```cpp
struct FoundComment {
  std::string DeclName;
  bool IsDefinition;
  std::string Comment;
  comments::DeclInfo::TemplateDeclKind TDK;
  // ... comparators are snipped ...
};
```
```cpp
  Action.Comments.push_back(FoundComment{
    ND->getNameAsString(), IsDefinition(D),
    RC ? RC->getRawText(Ctx.getSourceManager()).str() : "",
    RC->parse(Ctx, &Action.getCompilerInstance().getPreprocessor(), D)
         ->getDeclInfo()
         ->getTemplateKind()});
```

So for the following test case,
```cpp
  /// Aaa.
  template<typename T, typename U>
  void foo(T aaa, U bbb);

  /// Bbb.
  template<>
  void foo(int aaa, int bbb);
```

I didn't see the following failing
```cpp
  EXPECT_THAT(
      Comments,
      testing::ElementsAre(
          FoundComment{"foo", false, "/// Aaa.",
                       comments::DeclInfo::TemplateDeclKind::Template},
          FoundComment{
              "foo", false, "/// Bbb.",
              comments::DeclInfo::TemplateDeclKind::TemplateSpecialization}));
```

Did I misread anything from your last comment?

https://github.com/llvm/llvm-project/pull/108475