Disable Battery Saver when charging powered off

When a device is asleep or powered off, we don't get PowerStatus
updates, so we don't disable battery saver when charging.

BatterySaverController now uses a saved pref to detect jumps in charge
while running or across session restore which indicate that charging
occurred. Battery saver is disabled as if charging had been detected
directly.

Bug: b:319462921
Test: ash_unittests, manually charging while off and asleep.

Change-Id: I01d87eb7aaf8d020ffbbf2f851f155cccf71d432
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5377546


Reviewed-by: Michael Wojcicka <mwoj@google.com>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Charles Dick <cwd@google.com>
Reviewed-by: David Padlipsky <dpad@google.com>
Reviewed-by: Jiaming Cheng <jiamingc@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1281664}