refactor(devtools): run tslint --fix on devtools codebase

This commit runs tslint --fix with the angular/angular tslint configuration on the files inside the devtools codebase.

Notably, the file-header rule in `tslint.json` was missing a default attribute. This commit adds that default attribute and sets it to the
license header that is present in all files in this repo. After running tslint --fix with this default added, this commit added the license header to all files in the devtools directory. Note for the reviewer: the automatically added license headers were added as comments with the "/*!" prefix. Since we want these comments removed in builds, and the rest of the codebase uses "/**", a simple find and replace was performed on the devtools directory to change these prefixes to "/**".

devtools/src/iframe-message-bus.ts

@@ -1,3 +1,11 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
 import {Events, MessageBus, Parameters} from 'protocol';
 
 type AnyEventCallback<Ev> = <E extends keyof Ev>(topic: E, args: Parameters<Ev[E]>) => void;