[clang-tools-extra] [clang-tidy] Add new check 'misc-scope-reduction' (PR #175429)

[via cfe-commits]

vabridgers wrote:

I improved the diagnostics to include information about usages and suggested scope. I ran the check on an LLVM build finding a significant number of false positives that I suppressed (for-range was not originally included). Diagnostic usages are rate limited to 3 first usages then a count of remaining uses.

I'll take a run at the FP documented in the LIT then maybe turn my attention to finishing this up well enough for merging. 

Please let me know if you want more details on testing and anything else interesting to add to finish this up. Best

https://github.com/llvm/llvm-project/pull/175429