Add collectRssInBackground()

This change adds collectRssInBackground() and recordRssSampleLPf(),
which are intended to be drop-in replacements for their less-efficient
PSS counterparts. These methods are only used if the
removeAppProfilerPssCollection flag is enabled.

In general, references to PSS have been kept in places where they can
apply to RSS without much friction (e.g. getLastPssTime). In places
where PSS was actually recorded for use, method names were renamed to
include "OrRss" (e.g. getInitialIdlePss -> getInitialIdlePssOrRss).

If an app has set a PSS threshold for collecting a heap dump using
ActivityManager.setWatchHeapLimit(), Debug.getPss() is called if the
build is debug or the app is debuggable. This is done _in addition_ to
the RSS read, but should be a relatively small cost compared to the
decrease in PSS reads overall.

The threshold for downgrading a service to a service B in OomAdjuster
is increased by a default 1.5 when the flag is enabled to account for
RSS > PSS. This value can be updated in device-specific configs, or on
the command line with:
device_config put activity_manager pss_to_rss_threshold_modifier <value>

This flag is still disabled, so this change will have no effect once
submitted. However, before the flag is flipped on in any capacity, we
should notify android-chatty that the PSS info in logs/dumps will
change in case these are being read for dashboards/metrics/etc.

Lastly, reportCachedKill() has been removed from ProcessProfileRecord
and ProcessState because while they seem to report AppProfiler-collected
PSS to WW, they are actually unused.

Test: - Check with test logs that collectRssInBackground() is called
        when the feature flag is enabled.
      - Check that device_config put activity_manager
	pss_to_rss_threshold_modifier <value> propagates to AM.
Bug: 296454553
Change-Id: Ia4c4e14d7fb116e75857ea92c9fa2d2f534355f1