Find/Replace overlay: fix Ctrl+F6 crash on Linux

Avoid being stuck in an event loop by reacting asynchronously to part
activation events.
Additionally, manually give focus to the editor part after switching.
This behavior is default on windows but not consistent on Linux.

fixes #1951

bundles/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/texteditor/FindReplaceOverlay.java

@@ -236,21 +236,32 @@ public void controlResized(ControlEvent e) {
 	private IPartListener partListener = new IPartListener() {
 		@Override
 		public void partActivated(IWorkbenchPart part) {
-			if (getShell() != null) {
-				getShell().setVisible(isPartCurrentlyDisplayedInPartSash());
-			}
+			Display.getDefault().asyncExec(new Runnable() {
+				@Override
+				public void run() {
+					adaptToPartActivationChange();
+				}
+			});
 		}
 
 		@Override
 		public void partDeactivated(IWorkbenchPart part) {
-			// Do nothing
+			Display.getDefault().asyncExec(new Runnable() {
+				@Override
+				public void run() {
+					adaptToPartActivationChange();
+				}
+			});
 		}
 
 		@Override
 		public void partBroughtToTop(IWorkbenchPart part) {
-			if (getShell() != null) {
-				getShell().setVisible(isPartCurrentlyDisplayedInPartSash());
-			}
+			Display.getDefault().asyncExec(new Runnable() {
+				@Override
+				public void run() {
+					adaptToPartActivationChange();
+				}
+			});
 		}
 
 		@Override
@@ -264,6 +275,34 @@ public void partOpened(IWorkbenchPart part) {
 		}
 	};
 
+	private void adaptToPartActivationChange() {
+		if (getShell() == null || targetPart.getSite().getShell() == null) {
+			return;
+		}
+
+		getShell().setVisible(isPartCurrentlyDisplayedInPartSash());
+
+		targetPart.getSite().getShell().setActive();
+		targetPart.getSite().getPart().setFocus();
+
+		if (!(targetPart instanceof StatusTextEditor)) {
+			return;
+		}
+
+		StatusTextEditor textEditor = (StatusTextEditor) targetPart;
+		Control targetWidget = textEditor.getSourceViewer().getTextWidget();
+
+		Display.getDefault().asyncExec(new Runnable() {
+			@Override
+			public void run() {
+				if (targetPart.getSite().getShell() == null) {
+					return;
+				}
+				targetWidget.forceFocus();
+			}
+		});
+	}
+
 	private boolean isPartCurrentlyDisplayedInPartSash() {
 		IWorkbenchPage activePage = PlatformUI.getWorkbench().getActiveWorkbenchWindow().getActivePage();