[clang-tools-extra] [clang-tidy] Add a new check 'performance-string-view-conversions' (PR #174288)

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EugeneZelenko wrote:

> > lgtm, one nit
> 
> Thanks for all your patience with this PR) Is it Ok to merge or should I wait for one more reviewer, for example EugeneZelenko?

Documentation is fine for me, but I'm wrong person to judge implementation.

https://github.com/llvm/llvm-project/pull/174288