Added a TypeScript definition for computeSize

lib/index.d.ts

@@ -732,6 +732,14 @@ declare class Realm {
      */
     compact(): boolean;
 
+    /**
+     * Computes the aggregated size of all objects and their history in the Realm.
+     *
+     * Note that this will traverse the Realm and might be expensive for large Realms.
+     * @returns {number} the computed size in bytes.
+     */
+    computeSize(): number;
+
     /**
      * Write a copy to destination path
      * @param path destination path