Refactor MediaPlayerBase's notify

Test: make cts -j123 && cts-tradefed run cts-dev -m \
CtsMediaTestCases --compatibility:module-arg \
CtsMediaTestCases:include-annotation:\
android.platform.test.annotations.RequiresDevice

Bug: 70546581
Change-Id: Ia3a8eb99c2faf6935c63800ba08f65970cede48e
(cherry picked from commit 082e4f75)