chore(*): get rid of Bower in favor of Yarn aliases & checked-in packages

Bower was used to install multiple versions of jQuery which is now handled
using Yarn aliases. The remaining two packages, closure-compiler and
ng-closure-compiler were installed from zip files which is not supported by Yarn
(see https://github.com/yarnpkg/yarn/issues/1483); the first of them exists
on npm as the google-closure-compiler but only versions newer than we used are
published and they don't work with ng-closure-compiler so - instead - both were
checked in to the repository.

Fixes #16268
Fixes #14961
Ref yarnpkg/yarn#1483

TRIAGING.md

@@ -95,7 +95,7 @@ You can mention him in the relevant thread like this: `@btford`.
 
 > Thanks for submitting this issue!
 > Unfortunately, we don't think this functionality belongs in core.
-> The good news is that you could easily implement this as a third-party module and publish it on Bower and/or to the npm repository.
+> The good news is that you could easily implement this as a third-party module and publish it to the npm registry.
 
 
 ## Assigning Work