Add Context.createContextAsUser()

Without it, apps (mainline modules) will need to use createPackageContext...,
which is a bit painful.

Bug: 142472686
Test: atest android.content.cts.ContextTest#testCreateContextAsUser
Change-Id: Id640e03862462724df1a4a3101f0b08faafba22f
(cherry picked from commit b844001d6a8f0b10b2f379fd5bcdea8e896e7de7)
Merged-in: Id640e03862462724df1a4a3101f0b08faafba22f
6 files changed