[clang-format] [RELAND] Remove the dependency on frontend

Summary: relanding {D68969} after it failed UBSAN build caused by the passing of an invalid SMLoc() (nullptr)

Reviewers: thakis, vlad.tsyrklevich, klimek, mitchell-stellar

Reviewed By: thakis

Subscribers: merge_guards_bot, mgorny, cfe-commits

Tags: #clang-format, #clang

Differential Revision: https://reviews.llvm.org/D69854