Use bundle-collapser to save bytes on the output object

Created by: davemevans

I noticed that the minified source still contains all the import paths for the dependencies of each module. The paths are just used as keys and are arbitrary so can be replaced with anything. Since Uglify never changes string literals, these are not minified in the output.

bundle-collapser does this key replacement, removing the path strings and replacing them with the numeric modules IDs already in use.

This saves ~27k on the minified library (~2.5k when gzipped) in return for a negligible increase in transpile time.

I have tested in the reference player and it works as expected but it would be ideal if a couple of others could sanity check and report back.