feat: Get registered ID for a given phone number (#483)

Exposes internal getNumberById function for easy usage.
This can help with dealing with brazilian numbers with the extra digit, always returning the correct ID.

This will probably eventually replace the current isRegisteredUser function.

Co-authored-by: Pedro Lopez <pedroslopez@me.com>

src/Client.js

@@ -712,6 +712,26 @@ class Client extends EventEmitter {
         }, id);
     }
 
+    /**
+     * Get the registered WhatsApp ID for a number. 
+     * Will return null if the number is not registered on WhatsApp.
+     * @param {string} number Number or ID ("@c.us" will be automatically appended if not specified)
+     * @returns {Promise<Object|null>}
+     */
+    async getNumberId(number) {
+        if(!number.endsWith('@c.us')) {
+            number += '@c.us';
+        }
+
+        try {
+            return await this.pupPage.evaluate(async numberId => {
+                return window.WWebJS.getNumberId(numberId);
+            }, number);
+        } catch(_) {
+            return null;
+        }
+    }
+
     /**
      * Create a new group
      * @param {string} name group title