Enforce @TargetLocations annotation

[mernst]

If qualifier Q has a @TargetLocations meta-annotation and the programmer writes @Q at any location that is not listed in Q's @TargetLocations meta-annotation, then the Checker Framework should issue a warning. This warning may be suppressed (say, for making default annotations explicit in test cases).

(Issue ported from #515 which had become cluttered with other discussion.)

[Maxi17]

@mernst @smillst
Fixing this issue, I wanted to ask if some annotations need more @TargetLocations arguments.
For example, @BottomVal can be used on parameters too, even though it doesn't have TypeUseLocation.PARAMETER as argument to @TargetLocations (on fields too).
You can see my progress here: my branch (any opinion about it before opening the PR against CF master would be appreciated). Thank you!

[smillst]

@Maxi17 It's possible that some annotations need more target locations, but I don't think @BottomVal is one of them. Note the target locations specify where an annotation may be written by a programmer, but a type system by refine or default regardless of the target location of a qualifier. So, your code should check for annotations explicitly written on trees, not that AnnotatedTypeMirror for elements. See the code in org.checkerframework.checker.lock.LockVisitor#issueErrorIfGuardSatisfiedAnnotationInUnsupportedLocation for an example.