ApexManager: Request apexservice only when needed

Replacing the reference to apexservice with individual requests allows the service to be dynamically stopped when not in use and started on demand.

Bug: 149060287
Test: atest --test-mapping system/apex/apexd
Test: atest ApexManagerTest
Change-Id: I2d2173a692ec95a7a35b5a24ca466917e59c1da3