next analyze: annotate polyfill modules in UI (#86062)
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
