Clean up logic to determine whether an annotation is a type annotation

#2298 added checks to ensure annotations and modifiers are ordered properly.
This duplicated some logic in BaseTypeVisitor.isTypeAnnotation that would be more properly put into AnnotatedTypes, which already containes an isTypeAnnotation method.
#2376 started work on this clean up, but is running into problems.
Solving this issue would reduce duplication and move logic to a consistent place.

Start by comparing BaseTypeVisitor.isTypeAnnotation with the existing AnnotatedTypes.isTypeAnnotation method. Read the changes and problems described in #2298 and #2376 before tracing how annotation and modifier ordering checks use this logic. Done means the duplicated logic is centralized in AnnotatedTypes and ordering checks continue to work.