Find/replace: add test for whole-word availability with inactive regex support

Whole-word search and regex mode are mutually exclusive when regex is
effectively active. However, activating regex mode on a target that does
not support regex has no effective impact -- the option is activated but
not available, so it must not restrict other options like whole-word search.

This is already the correct behavior: the availability check for whole-word
uses isAvailableAndActive(REGEX), which requires both availability and
activation, so merely activating regex on a non-capable target leaves
whole-word unaffected.

A test is added to explicitly document and protect this invariant.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: HeikoKlare

tests/org.eclipse.ui.workbench.texteditor.tests/src/org/eclipse/ui/internal/findandreplace/FindReplaceLogicTest.java

@@ -719,6 +719,19 @@ public void testWholeWordSearchAvailable() {
 		assertFalse(isConsideredWholeWord.test(""));
 	}
 
+	@Test
+	public void testWholeWordRemainsAvailableWhenUnavailableRegexIsActivated() {
+		IFindReplaceLogic findReplaceLogic= setupFindReplaceLogicObject(null);
+		findReplaceLogic.setFindString("word");
+		assertFalse(findReplaceLogic.isAvailable(SearchOptions.REGEX)); // null target has no regex support
+		assertTrue(findReplaceLogic.isAvailable(SearchOptions.WHOLE_WORD));
+
+		findReplaceLogic.activate(SearchOptions.REGEX);
+
+		// Activating an unavailable option has no effective impact, so whole-word must remain available
+		assertTrue(findReplaceLogic.isAvailable(SearchOptions.WHOLE_WORD));
+	}
+
 	@Test
 	public void testReplaceInScopeStaysInScope() {
 		TextViewer textViewer= setupTextViewer(LINE_STRING + lineSeparator() + LINE_STRING + lineSeparator() + LINE_STRING);