Use framework-appsearch-stubs instead of framework-appsearch

The framework.jar now uses framework-appsearch-stubs instead of the
implementation jar framework-appsearch. As a result, it no longer
exports private APIs of framework-appsearch.

This change also refactors the droidstubs module so that we use the
metalava args that are consistent with other stubs.

Bug: b/146218515
Test: m
Change-Id: Ia4ad349bc6297891f7cc23e2528a296d75326c5c