[IDE] Add file language icons to Duo context menu and tokens
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# Problem to solve
When using the context menu, make it easier to identify file languages by using their respective icons instead of the generic `document` icon.
See https://gitlab.com/gitlab-org/editor-extensions/meta/-/issues/223 for more details on the problem and user feedback.
## Why it's important
This will make it easier for users to scan and understand context sources when using Duo in the IDE.
## Proposal
Use [the file icons](https://design.gitlab.com/product-foundations/iconography/#file-and-folder-type-icons) already specified in Pajamas.
1. Match file language icons when in the `File` category of the context menu (e.g. `HTML, CSS, JS`)
2. Also use these new icons in the context tokens
## Example
| Description | Example |
| ------ | ------ |
| Context menu list | <img src="/uploads/4dfc994cf1707a0a258b5c3a78367f8a/Screenshot_2025-05-22_at_3.58.26_PM.png" width="300px"> |
| Context token | <img src="/uploads/18a022843052fc346badd24eeece7651/Screenshot_2025-05-22_at_3.58.16_PM.png" width="300px"> |
## Important links
- [Figma](https://www.figma.com/design/py1XaoxXhPpc1jFocBMUnx/%E2%AD%90-Duo-in-the-IDE--16983?node-id=3581-8990&t=qlJE8xkWORZTMdcK-1)
- [Prototype iteration 3](https://prototyping-939024.gitlab.io/) (to illustrate the concept, not a 1:1 spec)
issue