Enable non-"everything" stubs generation in java_api_library

This change adds support to generate non-"everything" (i.e. "runtime"
and "exportable") stubs in java_api_library, which generates the stubs
from the api signature files.

Unlike droidstubs module that generates "everything", "exportable" and
"runtime" stubs in a single module, java_api_library generates a single
set of stubs per module, which is set by the default-"everything"
property `stubs_type`. This is because java_api_library is responsible
for both generation and the compilation of the stubs srcjar, and
compilation of the stubs srcjar are done in separate java_library
modules for from-source stubs.

Utilization of this feature will be done in a follow up change that
generates the "exportable" java_api_library modules in java_sdk_library.

Test: m nothing --no-skip-soong-tests
Bug: 318009570
Change-Id: I1051544ac3bcdb3ba1f78bfec28eba4e9fad9c2d