Modify aconfig_declaration modules visibility

The aconfig_declaration modules that define the aconfig flags that the
source Java files depend on are exported to the droidstubs modules
defined in frameworks/base/api. Therefore, modify the visibility of
these modules so that the droidstubs modules can depend on the
aconfig_declaration modules.

Test: m nothing
Bug: 315027929
Change-Id: Ifa5b4a7231fb702bc61bc1be450a5fe01f2ebcda