Specify is_stubs_module property

This change specifies is_stubs_module property to a module that
provides stubs, so that the build system recognizes it and can be used
for inter-container dependency.

Test: m nothing
Bug: 338660802
Change-Id: I4a9da74f74fc3c40abd2d52028c86aca538d6e40
diff --git a/api/StubLibraries.bp b/api/StubLibraries.bp
index 12820f9..8dfddf0 100644
--- a/api/StubLibraries.bp
+++ b/api/StubLibraries.bp
@@ -1345,4 +1345,5 @@
         ":hwbinder-stubs-docs",
     ],
     visibility: ["//visibility:public"],
+    is_stubs_module: true,
 }