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 within and without the change on a
blueline 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