MediaProvider requires permissions that diverge from those
of a typical priv_app. This create a new domain and removes
Mtp related permissions from priv_app.

Bug: 33574909
Test: Connect with MTP, download apps and files, select ringtones
Test: DownloadProvider instrument tests, CtsProviderTestCases

Change-Id: I950dc11f21048c34af639cb3ab81873d2a6730a9

The new domain wasn't fully tested, and it caused many regressions
on the daily build.  Revert back to using "priv_app" domain until we
can fully test and re-land the new domain.

Temporarily add the USB functionfs capabilities to priv_app domain
to keep remainder of MtpService changes working; 33574909 is tracking
removing that from the priv_app domain.

Test: builds, boots, verified UI and downloads
Bug: 33569176, 33568261, 33574909
Change-Id: I1bd0561d52870df0fe488e59ae8307b89978a9cb

Also move necessary priv_app permissions into MediaProvider domain and
remove MediaProvider specific permissions from priv_app.

The new MtpServer permissions fix the following denials:

avc: denied { write } for comm=6D747020666673206F70656E name="ep0" dev="functionfs" ino=12326 scontext=u:r:priv_app:s0:c512,c768 tcontext=u:object_r:functionfs:s0 tclass=file permissive=1

denial from setting property sys.usb.ffs.mtp.ready, context priv_app

Bug: 30976142
Test: Manual, verify permissions are allowed
Change-Id: I4e66c5a8b36be21cdb726b5d00c1ec99c54a4aa4