[clang-tidy] RenamerClangTidy group redecls into 1 warning.

[clang-tidy] RenamerClangTidy group redecls into 1 warning.

This changes the behavious of `RenamerClangTidyCheck` based checks by grouping declarations of the same thing into 1 warning where it is first declared.
This cleans up clang-tidy output and prevents issues where 1 fix-it couldn't be applied, yet all other warnings(and fix-its) for the same declaration would be applied.
The old behaviour of forward declaring a class without defining it isn't affected, i.e. no warnings will be emitted for that case.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D82059