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.
Speed-up ObjCMethodDecl::getOverriddenMethods().

Use an newly introduce ASTContext::getBaseObjCCategoriesAfterInterface() which caches its
results instead of re-calculating the categories multiple times.