java_sdk_library use prebuilt jars for numeric sdk_version

Previously, when a library that used a numeric sdk version also
referenced a java_sdk_library it would use the current version of its
API. That was dangerous as there is an expectation that an app building
against a numbered version will also be targeted at that version and
so building against a later version of the API could hide runtime
incompatibilities.

This change will use prebuilt versions of the java_sdk_library's api
when being built for a numbered sdk version.

Bug: 148080325
Test: m droid
Change-Id: I3fd416553950785a443c1702e495a96debc33331