Fix overlogging of filter and section changes

The addition of a second round of filtering introduced a bug that would
cause the system to log false filter and section changes for all notifs
on every run of the pipeline.

Previously, we had logic like the following:
(assume that, in the previous run, entryA was filtered out by filter1
during the pre-finalized stage)

1. preGroupFilters run, nothing returns true. Set
entryA.mExcludingFilter to null. It changed! Log it.
2. preFinalizeFilters run, filter1 returns true. Set
entryA.mExcludingFilter to it. It changed! Log it.

NotifSections had a similar bug that would null out their assigned
section every time they were filtered out.

To solve this, we introduce an mPreviousExcludingFilter field on
NotificationEntry that will allow us to determine whether the filter
actually changed as compared to the previous run. We also move that
logging logic to the end of the pipeline.

To solve the sectioning issue, we just don't null out sections when the
entry is filtered out. Long-term, we should move to a system similar to
the one above, but that's more complicated.

Test: atest
Bug: 112656837
Change-Id: Ib78dbbb0346947210cc1b6b49547595895e9fce5