[AI] Use getOrPut to update the multi resource map (#7165)

That method is cleaner, and the intended way, of inserting a value into
a map if it's missing.

Tag: cleanup

Author: rlazo

firebase-ai/src/main/kotlin/com/google/firebase/ai/FirebaseAIMultiResourceComponent.kt

@@ -41,14 +41,14 @@ internal class FirebaseAIMultiResourceComponent(
 
   fun get(backend: GenerativeBackend): FirebaseAI =
     synchronized(this) {
-      instances[backend.location]
-        ?: FirebaseAI(
-            app,
-            backend,
-            blockingDispatcher,
-            appCheckProvider,
-            internalAuthProvider,
-          )
-          .also { instances[backend.location] = it }
+      instances.getOrPut(backend.location) {
+        FirebaseAI(
+          app,
+          backend,
+          blockingDispatcher,
+          appCheckProvider,
+          internalAuthProvider,
+        )
+      }
     }
 }