Limit permission MANAGE_MEDIA_PROJECTION to the SystemUI role

Signature permission only is too broad; the permission is intended only for
SystemUI to facilitate capture sessions.

Bug: 323008518
Test: atest WmTests:ContentRecorderTests
Test: atest WmTests:WindowManagerServiceTests
Test: atest WmTests:DisplayContentTests
Test: atest MediaProjectionTests
Test: atest CtsMediaProjectionTestCases:MediaProjectionManagerTest
Test: atest FrameworksServicesTests:MediaProjectionManagerServiceTest
Test: atest AppEnumerationInternalTests:AppEnumerationInternalTests
Test: atest DisplayServiceTests:DisplayManagerServiceTest
Flag: com.android.media.flags.limit_manage_media_projection
Change-Id: Icd5ff01749a6c56ca4cba63a827974373c933e44