[clang] [clang-tools-extra] [lldb] [Clang][AST][NFC] (`RecordDecl` -> `CXXRecordDecl`)`::isInjectedClassName` (PR #148195)

[Yanzuo Liu via cfe-commits]

zwuis wrote:

> > I'm not sure if I should update `llvm/include/llvm/Testing/Demangle/DemangleTestCases.inc` and `libcxxabi/test/DemangleTestCases.inc`.
> 
> Why would you need to? There are no changes to mangling/demangling here AFAICT

These files test demangling `RecordDecl::isInjectedClassName`, which will be out-of-date (I think) after merging this PR.

https://github.com/llvm/llvm-project/pull/148195