Relabel Project Explorer filter dialog OK as Apply, add search icon

[vogella]

Summary

• Rename the OK button in the Project Explorer "Filters and Customization" dialog (CommonFilterSelectionDialog) to "Apply", which better reflects that the action applies filter and content-extension changes to the view.
• Add SWT.ICON_SEARCH to the filter pattern Text in CommonFiltersTab so the search icon is shown next to the existing cancel icon.

Test plan

• Open the Project Explorer, run "Filters and Customization..." and verify the primary button is labeled "Apply"; confirm it still commits filter and content-extension selections and closes the dialog.
• Verify the filter text field in the "Pre-set filters" tab shows both a search icon (leading) and the cancel icon (trailing), and that typing still filters the list.

[github-actions]

Test Results

   840 files   -    12     840 suites   - 12   39m 51s ⏱️ - 14m 29s
 7 229 tests  -   670   6 988 ✅  -   668  241 💤  -  2  0 ❌ ±0 
18 405 runs   - 1 794  17 778 ✅  - 1 766  627 💤  - 28  0 ❌ ±0 

Results for commit 1be3d9c. ± Comparison against base commit 9b991c8.

This pull request removes 670 tests.

org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testBoundaries
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testBug156426
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testBug377417
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testCloseMatches
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testCloseMatches1
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testIncompleteMatch
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testIncompleteMatch1
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testNesting
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testPartitioned
org.eclipse.jface.text.tests.DefaultPairMatcherTest ‑ testSimpleMatchDifferentMatchers
…

[vogella]