Select the correct annotation in MWLinkTargetInputWidget

The solution to this problem was two-fold:
* Initialize the menu selection based on current annotation data
* Don't re-open the LinkTargetInput suggestions menu after choosing

It unfortunately involves assuming that setAnnotation will always synchronously emit 'change' events.

Bug: 65343
Change-Id: Ia92751add5ee59ba581141a31c8433c5e7e521a5
Merge "Select the correct annotation in MWLinkTargetInputWidget"