[clang-tools-extra] [clang-tidy] Add fix-it for C-style cast of nullptr (PR #173159)

[Victor Chernyakin via cfe-commits]

localspook wrote:

The change looks good, but please:
- add a release note in `clang-tools-extra/docs/ReleaseNotes.rst`
- add tests for the change in `clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-style-cast.cpp`
- edit your PR message to change `Fixes #<173147>` to `Fixes #173147` (that way, when this PR is merged, Github will close that issue automatically)

https://github.com/llvm/llvm-project/pull/173159