Changes pulled data to use Parcel objects.

Previously, pulled data was returned as a string. We instead
return the data as an array of StatsLogEventWrapper, which encodes
using the binary-encoded format liblog uses. StatsD uses the same
parsing as for pushed events to convert these. This CL also fixes
the parsing of log_msg since the strings were previously emptied
before we had a chance to read the values.

Note that the cpp-aidl can't support List of Parcelable, so we
have to return the results as an array.

Test: Manual using the new command in StatsService to print results.
Also created a new unit-test by creating a dummy pull code of -1,
but this test is deleted since it required creating a fake output in
StatsCompanionService.

Change-Id: I1cfb9ea081a59292a60e934e8527adc40982ed80