[clang-tidy] Generalize TransformerClangTidyCheck to take a rule generator.

Summary: Tidy check behavior often depends on language and/or clang-tidy options. This revision allows a user of TranformerClangTidyCheck to pass rule _generator_ in place of a rule, where the generator takes both the language and clang-tidy options. Additionally, the generator returns an `Optional` to allow for the case where the check is deemed irrelevant/disable based on those options.

Reviewers: gribozavr

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D63288

llvm-svn: 364442