[clang-tools-extra] [clang-tidy] Add modernize-nlohmann-json-explicit-conversions check (PR #126425)

[Congcong Cai via cfe-commits]

HerrCai0907 wrote:

I am not sure whether we should accept this kind of "common" used library's custom check in clang-tidy.

- powerful and easy used tools which can help lots of C++ dev
- longer CI time
- larger binary size

I think we should a guideline this kind of cases to avoid to waste contributors effort. It is frustrating to write code and find out it can't possibly be merged.
@PiotrZSL @5chmidti @carlosgalvezp @AaronBallman WDYT?


https://github.com/llvm/llvm-project/pull/126425