limited web extension support

[serkonda7]

The extension now is available and works on the web.
Features are limited to syntax highlighting and snippets.

[SSlinky]

I've not looked into this before. I don't know how to test it, build it, and my linter hates it, but it does appear to work. Going to approve based on the following:

• Small beer functionality that is already tested in standard.
• webextension.js doesn't need building so unless we add more functionality, esbuild doesn't need to consider it.