Allow media app-ops for gallery role holder

Previously, we used to give broader access than necessary to Gallery
apps by allowing them MANAGE_EXTERNAL_STORAGE appop. This CL replaces
that appop with the specific appops for types of media that gallery apps
should be interested in: images and video.

Fixes: 148146627
Test: manual - dumpsys appops --package com.google.android.apps.photos
shows the write media appops
Change-Id: Iaec3baa5c6165dcdd5841a6c133c4c2f5a254ab7