Resolve request permission call when permission already exists

Problem:
If permission is already enabled, the native call to `OneSignal.getNotifications().requestPermission(fallbackToSettings, Continue.with(...)` never suspends and the Continuation code block never runs. As a result, we would not be able to resolve the promise over the bridge.

Solution:
Before calling that method, do a permission check and return true early.

www/NotificationsNamespace.ts

@@ -73,6 +73,10 @@ export default class Notifications {
      * @returns {Promise<boolean>}
      */
     requestPermission(fallbackToSettings?: boolean): Promise<boolean> {
+        // if permission already exists, return early as the native call will not resolve
+        if (this.hasPermission()) {
+            return Promise.resolve(true);
+        }
         let fallback = fallbackToSettings ?? false;
 
         return new Promise<boolean>((resolve, reject) => {