Upgrade emulator to emu-master-dev build 6946397 am: f21f51c1f2 am: 9e78008876

Original change: https://android-review.googlesource.com/c/platform/prebuilts/android-emulator/+/1484716

Change-Id: If2508bb96fa0a1172e94c674b7800312d2d65e11