Flush Content Capture context updated event immediately

Since setLocusContext() usually manually set/reset by developer to update
the app state, it makes sense to trigger a flushing to deliver the
update events immediately.

Bug: 191169236
Test: manual, check the events flush immediately
Test: atest CtsContentCaptureServiceTestCases
Change-Id: I0c367ec083b96d60600ca375c2d70c53224e9b62

core/java/android/view/contentcapture/MainContentCaptureSession.java

@@ -760,7 +760,7 @@ public final class MainContentCaptureSession extends ContentCaptureSession {
 
     void notifyContextUpdated(int sessionId, @Nullable ContentCaptureContext context) {
         mHandler.post(() -> sendEvent(new ContentCaptureEvent(sessionId, TYPE_CONTEXT_UPDATED)
-                .setClientContext(context)));
+                .setClientContext(context), FORCE_FLUSH));
     }
 
     @Override