Replace webpacker with vite

[bkeepers]

I couldn't get the outdated version of webpack-dev-server running locally. This replaces it with vite, which is a much more modern tool built on top of esbuild. I also couldn't get the old eslint running. I didn't see anywhere it was being used, so I just updated to the latest version using the default config.

A note on commands:

• npm start still runs the demo in development mode
• npm run build still builds the library (so npm publish just works)
• npm run build:demo will build the demo for publishing
• npm run lint will run eslint

[!NOTE]
I know this library has been stagnant for a while, so I'm not sure if my recent PRs will be merged or not. In the meantime, I'll be maintaining a fork with all my improvements at chordbook/vexchords.