Add DPM API to request location provider enable

DPM can currently control the master location toggle, but cannot
influence the behavior of individual providers. This adds an API for
DPM (or other privileged entities) to request a provider to turn itself
on.

Practically, this is necessary to allow DPM to control network location,
which may be gated by additional consents. This change also renames some
internal location code to make clearer the distinction between provider
enabled and provider allowed: enabled = location on && allowed

Bug: 136219903
Test: CTS tests to be added
Change-Id: I05f03c976428f0f5a8a2cf627a84dc9e2baf3e67