Guard clipping to avoid resize artifacts in tree viewer

[arunjose696]

Setting the clipping region temporarily to the textBounds was originally added (https://bugs.eclipse.org/bugs/show_bug.cgi?id=291245 comment 25) to prevent images from being overdrawn when implementting RIGHT or CENTER column alignment support in StyledCellLabelProvider. However, enabling clipping causes artifact lines during tree resizing, as a temporary workaround the clipping call is now guarded and applied only in those alignment cases to avoid issues with resizing of columns.

Steps to reproduce
Step 0:Set monitor zoom to 175

1. Set monitor zoom to 175%.
2. Launch a runtime workspace.
3. In that runtime workspace, open the Debug Configurations dialog.
4. Go to the Plug-ins tab for another runtime workspace / Eclipse application.
5. Resize the ID column in the Features view. Artifact lines appear without this workaround.

Behavior without the fix

old.mp4

Behavior with the fix

new.mp4

Additionally this issue can also be reproduced with the snippet provided in vi-eclipse/Eclipse-Platform#548 (comment)

[github-actions]

Test Results

 3 018 files  ±0   3 018 suites  ±0   2h 16m 38s ⏱️ + 6m 14s
 8 249 tests ±0   8 001 ✅ ±0  248 💤 ±0  0 ❌ ±0 
23 667 runs  ±0  22 876 ✅ ±0  791 💤 ±0  0 ❌ ±0 

Results for commit 220ef94. ± Comparison against base commit b4b98c6.

♻️ This comment has been updated with latest results.

[akoch-yatta]

Tested with the Runtime and the mentioned Snippet. Adapted the Snippet to be able to test with TreeViewer and TableViewer. This PR works with both scenarios. TreeViewer doesn't properly work with SWT.RIGHT and SWT.CENTER when the first column is resized (at least in windows), but this is a pre-existing and not caused or worsened with this PR