Support Metalava in java_sdk_library

The metalava is supported instead of doclava. However, not all sdk
libraries are available now. So metalava_enabled property is added for
it.
when using metalava, DroidstubsFactory module will be created instead of
DroiddocFactory.

Test: make -j
Test: make apicheck
Bug: 117127012

Change-Id: I7fd10230bfe30a4ef4dceb1a4459145b674668cd