Expose BIND_NOT_PERCEPTIBLE service flag

Using this flag when binding to a service will
allow the bound process to be held at a low
oom_adj of 250, so that it can be expunged to
reclaim memory if a more user-visible app needs
it.

Use for bindings such as job services and other
connections that the caller can easily recover
from and restart if necessary.

Adjust the lmk thresholds to use this oom_adj
as one of the levels, so they're killed before
perceptible apps (such as foreground services).

Bug: 135219821
Test: CtsAppTestCases
      Manually check notification listener oom_adj
      and dumpsys activity services output

Change-Id: I9f6d0891d842e4d12f7995b9b1a8f57b0903a16d