Make Vite include sourcemaps of bundled dependencies

[rekmarks]

All @metamask/* dependencies ship sourcemaps. This should allow us to operate the Chrome debugger on original sources, but it does not; something is missing. We need to figure out what.

Preliminary research indicates that we need to fiddle with Vite's dependency optimization. A couple of relevant links:

• Dependency pre-bundling explainer
• Dependency optimization config options
• esbuild's source map docs
  • Vite uses esbuild for dependency pre-bundling / optimization.