Fix LaunchAppShowImeAndDialogThemeAppTest flakiness

Using tapping DialogThemedActivity may possible to get unexpected focus
change to hide the keyboard, also DialogThemedActivity self doesn't set
android:windowSoftInputState=stateUnchanged, that affects the test
verfication that we expeting IME layer should persist visible.

Fix it by adding stateUnchanged softInputState flag, and simply using
UiDevice#pressBack to dismiss dialog without touching unrelated focus
change.

Fix: 215884488
Test: atest LaunchAppShowImeAndDialogThemeAppTest \
        --rerun-until-failure 20

Change-Id: I4704dfa531836423dafc3f3ece1d3b80584ae7fa

tests/FlickerTests/src/com/android/server/wm/flicker/helpers/ImeAppAutoFocusHelper.kt

@@ -67,10 +67,9 @@ class ImeAppAutoFocusHelper @JvmOverloads constructor(
         val dialog = uiDevice.wait(
                 Until.findObject(By.text("Dialog for test")), FIND_TIMEOUT)
 
-        // Tapping outside of the dialog to dismiss
+        // Pressing back key to dismiss the dialog
         if (dialog != null) {
-            val dialogBounds = dialog.visibleBounds
-            uiDevice.click(dialogBounds.left, dialogBounds.top - 300)
+            uiDevice.pressBack()
             wmHelper.waitForAppTransitionIdle()
         }
     }

tests/FlickerTests/test-apps/flickerapp/res/values/styles.xml

@@ -36,5 +36,6 @@
         <item name="android:windowNoTitle">true</item>
         <item name="android:windowIsFloating">true</item>
         <item name="android:backgroundDimEnabled">false</item>
+        <item name="android:windowSoftInputMode">stateUnchanged</item>
     </style>
 </resources>