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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

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

Also, please be sure to add the matcher to `clang/lib/ASTMatchers/Dynamic/Registry.cpp` and a release note to `clang/docs/ReleaseNotes.rst`.

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