Decodes url escape sequences in hover preview `file:///` links like
escaped
spaces in the file path.

I'm working on an LSP and happened to be working with some files in a
directory with spaces. When adding Markdown links with `file:///` the
`%20` escape for spaces was being included verbatim in the path that Zed
tried to open.

I'm reusing the lines from `markdown_preview_view.rs` for decoding. In
the existing tests I don't see coverage for `file:///` links. If you'd
like some tests for this can you point me to any examples to start from?

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- Fixed decoding spaces and other escaped characters in `file://` links
used in hover popovers

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Co-authored-by: dino <dinojoaocosta@gmail.com>