rust: Add ref to generated sources (aidl, bindgen)

Test: SOONG_GEN_RUST_PROJECT=1 m nothing; Edit
  system/security/keystore2/selinux/src/lib.rs;
  Check name resolution in IDE.
Bug: 168263887
Change-Id: Icbbf176c4355c3043807ce3fe0c3967c4a1374e2
diff --git a/rust/testing.go b/rust/testing.go
index ee303ed..42b0da1 100644
--- a/rust/testing.go
+++ b/rust/testing.go
@@ -117,6 +117,7 @@
 	ctx.RegisterModuleType("rust_binary", RustBinaryFactory)
 	ctx.RegisterModuleType("rust_binary_host", RustBinaryHostFactory)
 	ctx.RegisterModuleType("rust_bindgen", RustBindgenFactory)
+	ctx.RegisterModuleType("rust_bindgen_host", RustBindgenHostFactory)
 	ctx.RegisterModuleType("rust_test", RustTestFactory)
 	ctx.RegisterModuleType("rust_test_host", RustTestHostFactory)
 	ctx.RegisterModuleType("rust_library", RustLibraryFactory)