Generalize CovariantReturnTypeMultiHandler

The CovariantReturnTypeMultiHandler handles repeated instances of the
CovariantReturnType annotation on the same annotatable element. This
change generalizes the class so that it can work with any repeatable
annotation.

Bug: 119861512
Test: atest class2greylisttest, m -j20 framework
Change-Id: Id42ccc0a335f65701f81ec3fec201258e829f5ae