Change folder name to google__markerclustererplus to match scoped package (#42121)

* Change folder name

* Rename tests file

types/google__markerclustererplus/tsconfig.json

@@ -19,6 +19,6 @@
     },
     "files": [
         "index.d.ts",
-        "markerclustererplus-tests.ts"
+        "google__markerclustererplus-tests.ts"
     ]
-}
+}