problems(js): add “2693. Call Function with Custom Context”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/js/call-function-with-custom-context.js

@@ -0,0 +1,13 @@
+/**
+ * @param {Object} context
+ * @param {any[]} args
+ * @return {any}
+ */
+Function.prototype.callPolyfill = function(context, ...args) {
+    return this.apply(context, args);
+};
+
+/**
+ * function increment() { this.count++; return this.count; }
+ * increment.callPolyfill({count: 1}); // 2
+ */