[CIR] Fix some clang-tidy problems in CIR (#125128)
This adds a .clang-tidy file to the clang/lib/CIR/FrontendAction
directory, moves and updates the incorrectly located
include/clang/CIR/FrontendAction .clang-tidy file, and updates two files
from a recent commit to bring them into conformance with previously
agreed upon rules for where to use LLVM naming conventions and where to
use MLIR naming conventions.
