Fix imeLayerAndImeSnapshotVisibleOnScreen flaky

In case IME-snapshot removed and the assertion can't verify IME-snapshot
visible from the next frame, fix the assertion by verifying both
IME-snapshot and IME are invisible in the end.

Fix: 228947097
Test: atest FlickerTests:CloseImeEditorPopupDialogTest \
         --rerun-until-failure 20
Change-Id: I1d945cd10761af1c7dad9154a550e69bf4d481ee

tests/FlickerTests/src/com/android/server/wm/flicker/ime/CloseImeEditorPopupDialogTest.kt

@@ -91,6 +91,7 @@ class CloseImeEditorPopupDialogTest(private val testSpec: FlickerTestParameter)
                     .then()
                     .isVisible(FlickerComponentName.IME_SNAPSHOT)
                     .then()
+                    .isInvisible(FlickerComponentName.IME_SNAPSHOT)
                     .isInvisible(FlickerComponentName.IME)
         }
     }