Reroute surfaceflinger pulled atoms

Add a binder interface for pulling surfaceflinger atoms, and make
timestats return a vector of bytestring for the result of a pull,
instead of an AStatsEventList. This is part of a topic to reroute the
surfaceflinger pullers through system server to break surfaceflinger's
dependencies on libstatpull/libstatssocket. This will help enable
removing statsd from the bootstrap apexes.

Test: statsd_testrive 10062 10063
Test: updated the unit tests
Test: atest libsurfaceflinger_unittest
Bug: 184698814
Change-Id: I417b43dd6974d5f00cdb37215cccebf176525932