[clang] [clang-tools-extra] Move isLocal AST matcher to ASTMatchers (PR #117521)

[Congcong Cai via cfe-commits]

https://github.com/HerrCai0907 commented:

- Try to search usage of `isLocalVarDecl` in other checks and replace them with this one.
- Add some test cases of this matcher.

https://github.com/llvm/llvm-project/pull/117521