This PR changes the theme loading to use the JSON themes bundled with
the binary rather then the Rust theme definitions.
### Performance
I profiled this using `cargo run --release` to see what the speed
differences would be now that we're deserializing JSON:
**Before:** `ThemeRegistry::load_user_themes` took 16.656666ms
**After:** `ThemeRegistry::load_user_themes` took 18.784875ms
It's slightly slower, but not by much. There is probably some work we
could do here to bring down the theme loading time in general.
Release Notes:
- N/A
This PR decouples the generation of licenses for the themes we ship from
the TypeScript theme definitions.
For now, we are embedding the license information for the themes in the
`theme_importer`, and emit a combined `LICENSES` file in the `theme`
crate whenever we import themes. This is also where we check that each
theme has a valid license.
We then use this `LICENSES` file when building up the global license
file for Zed.
This decoupling is one step towards us being able to delete the old Zed1
styles.
Release Notes:
- N/A
