Add aconfig_declarations property to droidstubs and java_sdk_library

In consideration of the incremental build performance, this change let
droidstubs and java_sdk_library (which generates droidstubs per api
scope) modules to specify `aconfig_declaration` modules where the
dependent flags are defined in via the "aconfig_declarations" property,
opposed to passing uniform "all_aconfig_declaration"-generated flag
arguments to metalava.

When "aconfig_declarations" property is defined for java_sdk_library
modules, the property is passed to the generated droidstubs modules.

When "aconfig_declarations" property is defined for droidstubs modules,
the all aconfig_declaration modules listed in the property are listed as
deps, all cache protobuf files are gathered and metalava-consumable
flags are generated in "revert-annotations.txt".

Although this change introduces scalable implementation to easily
support generation of the "runtime" stubs corresponding flags, actual
support of the runtime flags/stubs will be done in future changes. This
change mostly focuses on the generation of the "exportable" flags.

Utilization of the generated "exportable" flags will be done in future
changes.

Test: go test ./java
Bug: 315485740
Change-Id: I37becd1b9dd9069d7ac4abed130906df30b3fdf4