[Compare] Apply editor selection colors to merge viewer panes

[tobiasmelcher]

Respect the configured selection foreground/background colors from editor preferences in the TextMergeViewer, including live updates when preferences change.

[tobiasmelcher]

The selection background/foreground colors set in the preferences under General->Editors->Text Editors were only used in the "Java Compsare" view, not in the "Text Compare". This pull request fixes this issue.

[github-actions]

Test Results

    54 files  +    5      54 suites  +5   35m 42s ⏱️ + 2m 41s
 4 666 tests ±    0   4 644 ✅ ±    0   22 💤 ±0  0 ❌ ±0 
11 892 runs  +1 183  11 739 ✅ +1 183  153 💤 ±0  0 ❌ ±0 

Results for commit f72e421. ± Comparison against base commit 327e3b8.

[iloveeclipse]

The selection background/foreground colors set in the preferences under General->Editors->Text Editors were only used in the "Java Compsare" view, not in the "Text Compare". This pull request fixes this issue.

Is this screenshot before or after the change?

[tobiasmelcher]

We got this error reported from Mac users when working with the dark theme. Following screenshots show the state without this pull request.

Here the preference page showing the selection foreground/background colors:

In the "Java Compare" editor these color settings are correctly taken:

After switching to the "Text Compare" the selection colors are not correct (they are from the light theme):

This pull request ensures that the correct selection foreground/background colors are also taken in the "Text Compare" view of the compare editor.

[iloveeclipse]

LGTM