[clang-tools-extra] Add migration shell script to modernize-type-traits.rst (PR #202526)

[Baranov Victor via cfe-commits]

vbvictor wrote:

> I see. Is there a suitable place for something like this? Or are they just something we can't share?

I can't think of a place right now where users a) wouldn't expect any support b) easily discoverable. I think clang-tidy shouldn't promote any hacky ways to do transformations at all. We care about checks and correctness. 

https://github.com/llvm/llvm-project/pull/202526