Find/replace overlay: Read regex option from model instead button state

The regex search button state is synchronized from the find/replace
logic's option state via a listener, so decorate() reading the button's
selection depends on that synchronization having happened. Reading the
option directly from the logic removes this hidden ordering dependency
and is consistent with how the other consumers (e.g., content assist
availability) already query the model.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: HeikoKlare

bundles/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/internal/findandreplace/overlay/FindReplaceOverlay.java

@@ -1039,7 +1039,7 @@ private void updateContentAssistAvailability() {
 	}
 
 	private void decorate() {
-		if (regexSearchButton.getSelection()) {
+		if (findReplaceLogic.isAvailableAndActive(SearchOptions.REGEX)) {
 			SearchDecoration.validateRegex(getFindString(), searchBarDecoration);
 		} else {
 			searchBarDecoration.hide();