Add test scan message during Frontend.scan in the Frontend default impl

Note that this CL also fixes the broken Tuner 1.0 VTS due to the
filter testing events, which trigger the Tuner 1.0 VTS to read data
from the events meta data

Test: atest android.media.tv.tuner.cts
Test: atest VtsHalTvTunerV1_0TargetTest
Test: atest VtsHalTvTunerV1_1TargetTest

Bug: 181152149
Bug: 181242574
Change-Id: Ic6416e085dc2b81c3410db9e08fcea03cb8813d2