Fix MediaPlayer device-aware session id configuration.

Factory .create methods shouldn't implicitly generate
new audio session id, but pass AUDIO_SESSION_ALLOCATE
instead.

This will case the MediaPlayer constructor to generate
audio session id when needed, but won't prevent it
from using a device-specific audio session id if
there's one asociated with the context.

Bug: 298002296
Test: atest MediaPlayerUnitTest

Change-Id: I4947c09c9ab3ba905c6016466b45fc107ee7e2e0