Set TvBottomSheetActivity as unrestricted keep-clear area

This makes the Tv Pip move away from the dialog in order to not cover
its content

Bug: 227596282
Test: manual: start activity in Pip; start Duo and send:
      adb shell cmd sensor_privacy enable 0 microphone && \
      adb shell appops start com.google.android.apps.tachyon 27
Change-Id: Ifb0a11cc6c09b2b088d8a28c6016b831f5c57ac9