We currently have all those fields in AnnotatingParser::Context. They
are not inherited from the Context object for the parent scope. They
are exclusive. Now they are replaced with an enum.
`InCpp11AttributeSpecifier` and `InCSharpAttributeSpecifier` are not
handled like the rest in ContextType because they are not exclusive.
Reviewed By: curdeius, MyDeveloperDay, HazardyKnusperkeks, owenpan
Differential Revision: https://reviews.llvm.org/D121907