Depend on exportable mainline module stubs for doc generation

This change modifies the dependency graph of framework-doc-stubs to
depend on the exportable stub source jar of the mainline modules,
so that the flagged apis symbols are not elided.

Test: m doc dist && unzip -l out/dist/offline-sdk-docs-docs.zip | grep "android/configinfrastructure/aconfig"
Bug: 377585897
Change-Id: I2de643c27417a0ccb21016a3bc495127f3a30f81