V2 HMR

[aklinker1]

Couple of comments:

1. There can only be 1 dev server running at a time
2. We can't start Vite in dev mode because the manifest-loader plugin needs to effectively build everything so it can output a manifest with all the outputs listed in it
3. HMR only works for HTML pages, like V1
4. From the client pages, we can't load the scripts from http://localhost:3000 because of Chrome's rules against loading external code. It just blocks the file from being downloaded

So instead of serving a file over localhost when there's a change, we write that file to the output director and send a message to the client telling it to HMR, but based off a file path instead of a URL (http://localhost:3000/popup/index.js → /popup/index.js). These files can be loaded correctly!

Todo

• [x] Spin up server when running with HMR enabled
• [x] Write files to server instead of hosting them on localhost
• [x] Write entry point "templates" while loading the scripts and CSS files
• [x] Handle updates on the client side

[aklinker1]

This is working, but the code is a mess. I'll redo this PR