feat: sync multiselect of branches and tags with commit list

[Danielku15]

See #2004

Old Behavior: If one branch is selected in the sidebar, the respective commit was selected in the commit list.

New Behavior: All selected branches or tags are synced to the commit list enabling branch diffing by selecting the branches in the sidebar.

Further details: To keep the change focused I didn't rework the sidebar further to also allow selecting tags and branches across the "groups" (e.g. selecting a tag and a branch). This could be a second extension.

I tried to follow the existing principles how the components and viewmodels already communicate between them. Architecturally the selection could be synced better via managing a central observable collection to which all components contribute their selections. But that's not how SourceGit currently works. I didn't want to rework too much but focus on the feature.

Not perfect, but definitely a improvement.

Demo:

SourceGit_u39iBWabEW.mp4

[love-linger]

I do not like this feature.

Since the RevisionCompare page does not show which revision is left or right side, and these selected branches/tags may point to the save revision, it is not really useful as expected.

For example, when selecting branch A, B, C (the HEAD of C and B points to the same revision/commit), the Revision Compare page shows two infos. But it not easy to find out which is A.

Here is the current approach of SourceGit:

• When comparing two revisions (selected commits in HISTORY page), it is easy to checkout which revision is left or right side.
• When choosing Compare with HEAD, there's a HEAD badge to show which side is HEAD commit.
• When choosing Compare with Worktree, there's a Worktree badage to show which side is Worktree.
• When choosing a branch to compare with current branch, the Branch Compare windows shows the position of these two branch.