Introduce a new FGS type for media processing.

This new type should be used for CUJs related to photo or video editing
and processing.

The use of this type will be time-limited by a new callback API will be
introduced in a follow-up change.

Bug: 317788011
Test: atest ActivityManagerForegroundServiceTypeTest
Change-Id: I8f79905f5cd35116f0cb20451827a8a95924867d