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
diff --git a/api/api.go b/api/api.go
index 29083df..aa89c24 100644
--- a/api/api.go
+++ b/api/api.go
@@ -428,8 +428,9 @@
 
 func createPublicStubsSourceFilegroup(ctx android.LoadHookContext, modules proptools.Configurable[[]string]) {
 	props := fgProps{}
-	props.Name = proptools.StringPtr("all-modules-public-stubs-source")
-	props.Device_common_srcs = createSrcs(modules, "{.public.stubs.source}")
+	props.Name = proptools.StringPtr("all-modules-public-stubs-source-exportable")
+	transformConfigurableArray(modules, "", ".stubs.source")
+	props.Device_common_srcs = createSrcs(modules, "{.exportable}")
 	props.Visibility = []string{"//frameworks/base"}
 	ctx.CreateModule(android.FileGroupFactory, &props)
 }