Speed up build time (where is time spent? minify, 3x type checking, duplicate phet-io code imports)

[samreid]

A recent build of density with brands: phet,phet-io took 2m13s on MacBook Air M1

~/phet/root/density$ time grunt --brands=phet,phet-io
Running "default" task

Running "lint-all"
Linting completed successfully.

Running "report-media"

Running "clean"

Running "build"
Building runnable repository (density, brands: phet, phet-io)
Building brand: phet
>> Webpack build complete: 6353ms
>> Production minification complete: 13399ms (4723566 bytes)
>> Debug minification complete: 1ms (29449520 bytes)
Building brand: phet-io
>> Webpack build complete: 2018ms
>> Production minification complete: 10129ms (4742546 bytes)
>> Debug minification complete: 0ms (29882364 bytes)

Done.

real	2m13.044s
user	2m18.095s
sys	0m13.699s
~/phet/root/density$