Mark FocusHandlingTest#testOnStartInputCalledOnceIme flaky

We know this test has been flaky for a while.

Let's mark it with @FlakyTest annotation so that they can know that
the team is aware of it.

Bug: 129246377
Bug: 149246840
Test: make -j CtsInputMethodTestCases
Change-Id: Ifc38b5a824e681caa60a8a5aec0e0ddf08981127
diff --git a/tests/inputmethod/src/android/view/inputmethod/cts/FocusHandlingTest.java b/tests/inputmethod/src/android/view/inputmethod/cts/FocusHandlingTest.java
index 9b04e13..674463e 100644
--- a/tests/inputmethod/src/android/view/inputmethod/cts/FocusHandlingTest.java
+++ b/tests/inputmethod/src/android/view/inputmethod/cts/FocusHandlingTest.java
@@ -48,6 +48,7 @@
 import android.widget.TextView;
 
 import androidx.test.InstrumentationRegistry;
+import androidx.test.filters.FlakyTest;
 import androidx.test.filters.MediumTest;
 import androidx.test.runner.AndroidJUnit4;
 
@@ -95,6 +96,7 @@
         return TEST_MARKER_PREFIX + "/"  + SystemClock.elapsedRealtimeNanos();
     }
 
+    @FlakyTest(bugId = 149246840)
     @Test
     public void testOnStartInputCalledOnceIme() throws Exception {
         try (MockImeSession imeSession = MockImeSession.create(