Introduce SourceManager::getDecomposedIncludedLoc, that returns the "included/expanded in" decomposed location of the given FileID.

The main benefit is to speed-up SourceManager::isBeforeInTranslationUnit which is common to query
the included/expanded location of the same FileID multiple times.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179435 91177308-0d34-0410-b5e6-96231b3b80d8