- modify UnresolvedElementsSubProcessor.createTypeRefChangeProposal()
  method to check if a type it determines requires an import is actually
  a nested class in the same compilation unit in which case simply
  change the reference to fully qualified
- add new QualifyTypeProposal class
- add new test to UnresolvedTypesQuickFixTest

Change-Id: I60d73b436dfcf4b862cb92126d85e525617532da
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.ui/+/186734
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Tested-by: Jeff Johnston <jjohnstn@redhat.com>
Reviewed-by: Jeff Johnston <jjohnstn@redhat.com>