[clang-tools-extra] [clang-tidy] Rename google-readability-casting to modernize-avoid-c-style-cast (PR #171058)

[via cfe-commits]

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+.. title:: clang-tidy - modernize-avoid-c-style-cast
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+modernize-avoid-c-style-cast
+============================
+
+Finds usages of C-style casts.
+
+https://google.github.io/styleguide/cppguide.html#Casting
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zeyi2 wrote:

I think this should be moved to the docs of `google-readability-casting` as suggested [here](https://github.com/llvm/llvm-project/pull/170986/files#r2595575019)

https://github.com/llvm/llvm-project/pull/171058