Change using Handler to using Executor

Change addOnActiveSessionsChangedListener and other APIs to use
Executor instead of Handler according to API council guideline.

Also move the listener parameter to the end of the list
of parameters to improve Kotlin-compatibility, since Kotlin allows
SAM, or Single Abstract Method, to be expressed as a trailing
lambda syntax.

Bug: 174762061
Test: build && atest android.media.cts.MediaSessionManagerTest
Change-Id: I556d400e86e4c05c6840e6835432a82ca3695774