[clang-tidy] Refactor IncludeInserter
Simplified how IncludeInserter is used in Checks by abstracting away the SourceManager and PPCallbacks inside the method registerPreprocessor.
Changed checks that use IncludeInserter to no longer use a std::unique_ptr, instead the IncludeInserter is just a member of the class thats initialized with an IncludeStyle.
Saving an unnecessary allocation.
This results in the removal of the field IncludeSorter::IncludeStyle from the checks, as its wrapped in the IncludeInserter.
No longer need to create an instance of the IncludeInserter in the registerPPCallbacks, now that method only needs to contain:
Also added a helper method to IncludeInserter called createMainFileInclusionInsertion, purely sugar but does better express intentions.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D83680