Enforce owner rights check to setSplashScreenTheme

In the normal cases, setSplashScreenTheme should only work while the
target package and the calling uid are from the same package and user.
Adding the checking to setSplashScreenTheme.

Bug: 206474016
Test: atest PackageManagerServiceTest
Test: atest CtsWindowManagerDeviceTestCases:SplashscreenTests \
        #testOverrideSplashscreenTheme
Change-Id: Ib9fb4214d8b14bfedd99a8e99849ca11fe97efe3
Merged-In: Ib9fb4214d8b14bfedd99a8e99849ca11fe97efe3