Add batterystats -c data to telephony bugreports

Telephony bugreports currently capture 'dumpsys batterystats' output,
but only in its human-friendly format.  While humans may enjoy that
format, Historian does not, and fails to properly load telephony
bugreports (including those triggered by LowPowerMonitor) as a result.
This makes it essentially impossible to use Historian when triaging/
analyzing telephony-style bugreports.

To enable Historian processing of telephony bugreports, this change adds
the 'checkin' format ("dumpsys batterystats -c") data along with the
existing entries.

ABT (Android Bug Tool) still doesn't properly list dumpsys sections in
its UI even with this change, but I think nothing short of a full,
comprehensive dumpsys run will make ABT happy.  And that's okay, because
all of the text content can still be navigated manually.

Bug: 111763716
Test: Triggered telephony bugreports with and without the change on an
appropriate device, manually verified that the checkin format data was
present with the code change in place, and loaded the bugreport into
Historian successfully.

Change-Id: Iba434bfd219c627cd3c058e549a627947d9ce501