[clang-tidy] Ignore namespaced and C++ member functions in google-objc-function-naming check 🙈

Summary: The google-objc-function-naming check applies to functions that are not namespaced and should not be applied to C++ member functions. Such function declarations should be ignored by the check to avoid false positives in Objective-C++ sources.

Reviewers: benhamilton, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: xazax.hun, cfe-commits

Differential Revision: https://reviews.llvm.org/D55101

llvm-svn: 348317