Empty Compare panes in Synchronize view

[eposse]

Issue and tracking information

Developer's time Estimated effort to fix (hours):

Developer's Actual time spent on fix (hours)

Issue reporter to provide a detailed description of the issue in the space below

When doing a comparison between a local model and a commit using the Synchronize view (not the Git Compare view), the left and right panes are empty even when selecting an element. See the attached screenshots.

However, it does seem to display the changes when the selected element is a conflict, or at least an incoming (right-to-left) conflict. See the attached screenshots.

This seems to be a regression, as it used to display correctly.

Steps to reproduce

1. Create a git repo
2. Create a model in the git repo
3. Create a new branch
4. Create conflicting changes between the main branch and the new branch; for example, in one branch change the Type of a Property in a Class, and in the other branch delete that property.
5. In the project explorer, right-click on the Papyrus model
6. Click on "Compare with > Branch, Tag, or Reference ..."
7. Select the branch to compare against and click [OK]
8. When asked to switch to the Team Synchronizing perspective accept.
9. In the Synchronize view on the left, unfold the project folder until you see the .uml file
10. Right-click the .uml file and select "Open in Compare Editor"
11. Navigate the model by either clicking and unfolding elements or using the toolbar buttons on the top-right.

Expected result

For every element change, the left and right panes must show the difference for that element.

Actual result

Only conflicting incoming (right-to-left) changes are displayed in the left and right panes.

Affects

streams/v2 and streams/v3

Environment

PapyrusCX 2.6.x PapyrusCX 3.0.0 Ubuntu 20.04

Screenshots

Compare in Synchronize view; non conflicting change selected:

Compare in Synchronize view; conflicting change selected:

[eposse]

Closing as it is a duplicate of #499.