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

[via cfe-commits]

vabridgers wrote:

> We should not post (probably unreviewed) AI text, https://llvm.org/docs/AIToolPolicy.html

I've removed the text I think was objectionable (since the comment was not specific). I reviewed the text and attributed Claude Sonnet as co-pilot in the commit header before posting, so not sure what the specific objection was. Please let me know if there's anything else I missed. 

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