[560861] Swapping content merge viewer don't swap phantoms

The target side when revealing phantom decorators don't return the
correct MergeViewerSide when the compare configuration is mirrored.

- Fix the method PhantomManager#getTargetSide(Match, View)

- Refactor DiagramContentMergeViewer class

- Creating Unit tests

Bug: 560861
Change-Id: I437293113ad2e5fe91ffb4977aaa52c975167d73
Signed-off-by: Glenn Plouhinec <glenn.plouhinec@obeo.fr>
22 files changed