Add end-to-end tests for @EnforcePermission

The current integration tests under system/tools/aidl mock
PermissionEnforcer and as such do not exercise the complete permission
checks. Set up a service app (service-app) which relies on the
annotation to protect its methods. A nested service is included to test
that permission checks propagate to same-process calls.

Bug: 269721152
Test: atest EnforcePermissionTests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b404eee1c159bd4bc2d5c0500a1996cfbceb2799)
Merged-In: I2d14f10333eabc385007216038dc487f83a4d21a

Change-Id: I446406aa0e7ce6de5745d870599d37706cc52cf9