[AVRCP] Skip GLOBAL_PRIORITY MediaSessions

MediaSession with GLOBAL_PRIORITY flag set is created by
Telecom to handle wired headset key events during call.

In Bluetooth, these key events go through HFP and not AVRCP
so we don't want to have them as active media session.

Bug: 266171157
Tag: #feature
Test: atest MediaPlayerListTest, MediaPlayerWrapperTest
Change-Id: Ie017ecd76da14aa955964b5c0daf2a83269c37d7