Pass in the user defined by Context.

The majority of Manager-style classes already use Context.getUserId()
when making calls into the OS, so clean up the remaining callers to
unify behind this strategy.

This gives @SystemApi developers a nice clean interface to interact
across user boundaries, instead of manually adding "AsUser" or
"ForUser" method variants, which would quickly become unsustainable.

Test: builds, boots
Bug: 72863821
Exempt-From-Owner-Approval: trivial changes
Change-Id: Ib772ec4438e57a2ad4950821b9432f9842998451