Fix strictMode violation in Accesibility Service

From Android R, using the WindowManager from non-ui context
violates the vm policy. It may cause incorrect window bounds
with the given floating window. AccessibilityService provides
Accesibility overlay usage that needs to set window token to
the windowManager. However, Setting it when the service is bounded
violates the policy.
To fixt it, we set the window token when developers get WindowManager
first time.

Bug: 175785781
Test: atest AccessibilityOverlayTest, use the test apk to check if
the warning message is shown in the log
      manual test to see if SelectToSpeak works well
Change-Id: Ia873488626aa4da111499282d1971f836cf111cd

Change-Id: Ia87df60c393bb0e40d85ced4184c78a09d7b427b