Added button to launch activity that resets directory access.

Test: ./gradlew preflight && ./gradlew assembleDebug && adb install -r \
      ./Application/build/outputs/apk/debug/Application-debug.apk && adb shell \
      am start com.example.android.scopeddirectoryaccess/.MainActivity

Bug: 63720392

Change-Id: I8bc5438ad9e9cfd9e1bcee8f38c830336d3c84ef
(cherry picked from commit 9331959d)