Add support for GopherJS on web

[kkoreilly]

Describe the feature

Using https://github.com/tinygo-org/tinygo for web could drastically reduce binary sizes, making it much more viable to use Cogent Core for websites. I tried to do this and ran into a bunch of issues with reflect slice headers and missing os functions, but we should look at this again and try to get it working at some point.

Relevant code

No response