Clean up OomAdjusterModernImpl

Reorganize OomAdjusterModernImpl for future changes.
Moved most logic into reusable helper methods and functional interface
implementations.

Reimplemented the reachable process collection step to use the same
code as the process traversal step. It is important that the traversal
algorithm for these two steps are identical (If the traversal step finds
a process the reachable step did not find, the wrong values could get
calculated).

Replaced the excluded client process collection step with just
evaluating the connections into the target and reachable processes.

Bug: 323376416
Test: atest MockingOomAdjusterTests
Change-Id: If61a700c092574b1fc3a7a456d89dd0e478d2672