Add Isolated Compilation service

Create a skeleton system service which will be used to run Isolated
Compilation using a system server classpath fragment in the CompOS
APEX.

This has no effect if the CompOS APEX is not present (i.e. isolated
compilation is not enabled).

Bug: 199147668
Test: starts up with CompOS present & not
Change-Id: I5ee853cfaf4d9633dd8db348d13e0dfe00bd4dca