Text hover doesn't work for cross references in annexes

[lwrage]

Summary
An annex library or subclause can reference, for example, a property. Hovering over the reference should show the property's AADL doc comment, but it doesn't show anything.

Expected behavior
Show hover text.

Actual behavior
No hover text shown.

Desktop (please complete the following information):

• OSATE Version: 2.12
• Operating System: all

[lwrage]

The issue is in code that finds the xtext node for an annex element. This is handled correctly for "go to definition" via ctrl+click and needs to be fixed separately for hover.
There may be other places that need a similar fix (mark occurrence?, rename?).