### What?
fix the import chain showing only modules relevant to the current route
fix module graph being merged by path. It's keyed by identifier now.
also add more info to import chain, e. g. layer info. and more details in tooltip.
For small routes, it can appear like the polyfill chunk takes up a sizable amount of data, but `polyfill-nomodule.js` is only sent to legacy browsers. This makes it clearer.
This PR enhances the bundle analyzer by adding visual indicators for polyfill chunks, and noting they're conditionally sent to modern or legacy browsers. The changes include:
- Adds a source map to polyfill chunks (for the large pre-bundled input only)
- Visually distinguished polyfill chunks in the treemap by lightening their color
- Added a "Polyfill" badge (other badges coming soon!) with text when viewing polyfill chunk details
<img width="388" height="227" alt="image" src="https://github.com/user-attachments/assets/bcebfba6-1e10-459a-9364-b6b8197cd3df" />
Fixes PACK-5826
This adds an interactive Treemap-style bundle analyzer app to the Next.js codebase and writes a copy to disk when `next build --experimental-analyze` is run.
* It's a separate app in `apps/bundle-analyzer` as `@next/bundle-analyzer-ui` that uses `output: 'export'` to export a purely static Next.js app
* These static resources are copied into Next.js's published `dist` directory in the `next` package itself. Users never depend on `@next/bundle-analyzer-ui`
* When users run `next build --experimental-analyze`, these static resources are copied into the user's `.next/diagnostics/analyze` along with the data payloads needed to visualize the user's app
In an upcoming PR, we'll add `next experimental-analyze` that will create analysis files without build artifacts, as well as optionally start a static file server.
Test Plan: Ran `next build --experimental-analyze` in a test app and ran a static file server to run it.
Will Binns-Smith
