ProcessList refactor

Moving code from ActivityManagerService to ProcessList for things
related to processes.

Only moving code now, will fix "deep links" in follow-up CLs.

Phase 1:
  Move process creation/removal code
  Move LRU structures

Next: Move oom_adj code

Bug: 111369273
Test: atest CtsAppTestCases
Change-Id: Icd369c3533b01ee8d40359ce6fe81c37df608c9a