[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:
```
Inserter.registerPreprocessor(PP);
```
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