Convert browser and generic to TS

Part of #335

src/utils/Generic.ts

@@ -0,0 +1,14 @@
+/**
+ * Generic utilities module with methods that can be helpful at different parts of the code base.
+ * @module xterm/utils/Generic
+ * @license MIT
+ */
+
+/**
+ * Return if the given array contains the given element
+ * @param {Array} array The array to search for the given element.
+ * @param {Object} el The element to look for into the array
+ */
+export function contains(arr: any[], el: any) {
+  return arr.indexOf(el) >= 0;
+};