feat: add support for injecting debug IDs

[timfish]

Debug IDs are detailed in the TC39 proposal.

Debug IDs are unique IDs generated from a deterministic hash of the source code which are then injected/included in both source and sourcemap. They can be used to easily identify the correct sourcemaps in production.

I've recently added support for injecting debug IDs to webpack, Rollup, and Rolldown and wanted to get them working in Vite too.

Since we're only concerned with production builds, I'd assumed it would work simply by passing the new Rollup output option:

import { defineConfig } from 'vite';

export default defineConfig({
  root: './src',
  mode: 'production',
  build: {
    outDir: './dist',
    sourcemap: true,
    rollupOptions: {
      output: {
        sourcemapDebugIds: true,
      }
    }
  }
});

Unfortunately this didn't work out-of-the-box with all output assets because in some cases, after Rollup output, buildImportAnalysisPlugin modifies the source code, updates the sourcemap and then outputs the new sourcemap with no debug ID.

In an Ideal World™ we would re-hash the source to get an updated ID and replace the debug ID injected by Rollup in the source and sourcemap. I don't know the Vite code that well but it looks like this would add a lot of code to Vite and might be overkill.

It looks like buildImportAnalysisPlugin is adding to the source code in a deterministic way so I have determined that it's likely safe to just retain the ID computed previously in Rollup and copy it to the new sourcemap.

I'll cc @lforst here since he wrote the proposal and will be able to confirm whether this compromise is ok.

To finish this PR:

• Types fixes to magic-string need to be merged, released and then released in Rollup feat: Include debugId in SourceMap types Rich-Harris/magic-string#294
• It needs some tests