Rename KeyEvent.isMediaKey() to isMediaSessionKey()

Since not all KEYCODE_MEDIA_* keycodes return true in isMediaKey(),
the naming can give confusion. This CL renames the method to
isMediaSessionKey() and revises its Javadoc.

Bug: 119789707
Test: make -j
Change-Id: I36786ccf5606977e6d971c13d77d950356561bda
6 files changed