Minify, compress, and possibly tree-shake assets

[peekxc]

Possibly a generalization / duplicate of #1665

When I load a basic shiny app w/ the cache disable, the download size for shiny.js is ~1 MB

The size of the minified file (shiny.min.js) shipped in the package is only 435 KB (though it is not loaded in the default app); a minified and Brotli-compressed version would be a mere 78 KB.

It would be nice if you fixed the include to the minified one, and perhaps consider pre-compressing all the js/css assets for speedy loading