Create aliases for stubs in build/bazel/api_surfaces

- Create the alias under the module-libapi directory. This is the
  api_surface that cc_stubs_suite maps to.
- Create the alias only for "current" (atleast for now)
- Create one alias for the stub shared lib, and another for its headers

Test: b build @api_surfaces//... (with aosp/2475091)
Change-Id: Ib004c2c34256f971e74d75317fa5fbbe7273720e

android/config.go

@@ -1837,3 +1837,14 @@ func (c *config) LogMixedBuild(ctx BaseModuleContext, useBazel bool) {
 		c.mixedBuildDisabledModules[moduleName] = struct{}{}
 	}
 }
+
+// ApiSurfaces directory returns the source path inside the api_surfaces repo
+// (relative to workspace root).
+func (c *config) ApiSurfacesDir(s ApiSurface, version string) string {
+	return filepath.Join(
+		"build",
+		"bazel",
+		"api_surfaces",
+		s.String(),
+		version)
+}