Add overview annotations to DiffEditorPage
Add overview annotations for added/removed lines in the unified
diff.
* Add annotations for the DiffRegions of a DiffDocument.
* Coalesce adjacent DiffRegions in DiffRegionFormatter.
* Fix a layout problem with the overview ruler when used in the
DiffEditorPage.
* Derive the annotation colors automatically from the line background
colors as set by the user preferences or by the current theme.
* When colors change, use invalidateTextPresentation() in DiffViewer
instead of refresh() in order to maintain display state (scroll
and caret position, selection, folding, etc.) refresh() would reset
all those and jump to the beginning of the document.
Bug: 447512
Change-Id: I25964fee73b97995895f0a6819fb93c8ccdfbf04
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>