[clang-tidy] Force LF newlines when writing files

The recommendation on Windows is to checkout from git with
core.autolf=false in order to preserve LF line endings on
test files.  However, when creating a new check this results
in modified files as having switched all the line endings on
Windows.  Write all files with explicit LF line endings to
prevent this.

Fixes #52968

Differential Revision: https://reviews.llvm.org/D117535