Make java_sdk_library phony target depend on its stub jar

Currently, the (from-text) stub jar depends on the check api timestamp
of the same api scope droidstubs. However, building the top level
sdk_library phony target does not trigger check api, as the top level
java_sdk_library "depends" on the stub submodules but the top level
phony target does not build the stubs generated by its submodule, nor
the top level java_sdk_library generate any output files.

In order to support the user's workflow of observing checkapi failure
after modifying the api by running `m <java_sdk_library name>`, this
change adds the paths to the stub jars as dependencies as the top level
java_sdk_library phony target.

Bug: 234113632
Test: modify source file api, run m <java_sdk_library name> and observe checkapi failure
Change-Id: Iccd42c8ef7d5de20f71c347455c1a90d83a6c70c