Use op package name as the calling package while start activities

Apps with system_uid are allowed to run on other system core
processes. With f9e5c9fe, the component was unable to start activities
since the calling package and the calling uid weren't the same app.

Bug: 169859652
Test: start activity on phone process from a shared system uid package
Change-Id: Ida27c7518fb81cb5a1ac654e86fb1918f962ebf8