Merge pull request #12680 from aluanhaddad/12678

Add ReadonlyArray<T>.includes to es2016.array.include.d.ts

Author: sandersn

src/lib/es2016.array.include.d.ts

@@ -7,6 +7,15 @@ interface Array<T> {
     includes(searchElement: T, fromIndex?: number): boolean;
 }
 
+interface ReadonlyArray<T> {
+    /**
+      * Determines whether an array includes a certain element, returning true or false as appropriate.
+      * @param searchElement The element to search for.
+      * @param fromIndex The position in this array at which to begin searching for searchElement.
+      */
+    includes(searchElement: T, fromIndex?: number): boolean;
+}
+
 interface Int8Array {
     /**
       * Determines whether an array includes a certain element, returning true or false as appropriate.