Create libstats_jni

This cl creates libstats_jni, puts the android_util_StatsLog class in it
to implement the jni StatsLog.writeImpl() call, and puts the library in
the statsd apex.

Right now, it does NOT load the library properly and therefore the
library is still in the platform. It needs to be removed from the
platform.

Test: boots
Test: adb shell cmd stats print-logs shows logs still flow
Bug: 147315667
Change-Id: I0a06b66d4640d00ee75bc273423b33dafc944b05