Move Rust Binder tests into libbinder TEST_MAPPING

We want the Rust tests to trigger when libbinder changes, in case any
changes affect the Rust API.

Bug: None
Test: cd frameworks/native/libs/binder && atest
Change-Id: I10278c192e8c7dd29bc22144bc95451300524cb5
diff --git a/libs/binder/TEST_MAPPING b/libs/binder/TEST_MAPPING
index 61a611d..dafc879 100644
--- a/libs/binder/TEST_MAPPING
+++ b/libs/binder/TEST_MAPPING
@@ -50,6 +50,14 @@
           "exclude-filter": "android.os.cts.StrictModeTest#testNonSdkApiUsage"
         }
       ]
+    },
+    {
+      "name": "libbinder_rs-internal_test"
+    }
+  ],
+  "postsubmit": [
+    {
+      "name": "rustBinderTest"
     }
   ]
 }