Fix multiple configuration changes in multiwindow

When in split-screen mode and activity handles configuration changes
it gets 2 onConfigurationChanged calls which originate from
ActivityManagerService#updateConfigurationLocked:
1. app.thread.scheduleConfigurationChanged calls to all process records
   send configuration of the whole screen for corresponding orientation,
   which leads to CONFIGURATION_CHANGED message in ActivityThread.
2. mStackSupervisor.resizeStackLocked call resizes both visible stacks and
   eventually ActivityThread receives ACTIVITY_CONFIGURATION_CHANGED
   message with correct configuration corresponding to space occupied in
   split-screen.

In this CL if component callback is an instance of Activity and it had
override config set - onConfigurationChanged will not be triggered unless
override config has changed.

Bug: 27948331
Change-Id: Ia73b045570b44eb5b351811bf6c4f63d78c3f909