This PR updates the `Model` to `Entity` also fixes the
`IndentGuidesStory`. In this
[commit](https://github.com/zed-industries/zed/commit/6fca1d2b0ba93cdbc3255657a990828a0f22b199),
`Entity<T>` replaces `View<T>`/`Model<T>`.

Other than this, I noticed the storybook fails on my MacOS and Ubuntu,
see error below

```
thread 'main' panicked at crates/gpui/src/colors.rs:99:15:
called `Result::unwrap()` on an `Err` value: no state of type gpui::colors::GlobalColors exists
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

This was resolved by explicitly specifying `GlobalColors` in Storybook.

Release Notes:

- N/A