Add folder_indicator setting to show chevron and folder icon together (#62393)

# Objective

- Enable panels to show chevron and icon at the same time.
- Closes #8661

## Solution

- Replaces `folder_icon` with a new `folder_indicator` which converts
from a boolean to enum (`both`, `chevron`, `icon`) for the three display
cases

## Testing

- gpui and migration tests had been applied

## 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 adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

## Showcase

### project panel

both | chevron | icon
--- | --- | ---
<img width="400" alt="both_project_panel"
src="https://github.com/user-attachments/assets/4c21e1a1-a7a4-4471-b7de-fe867373ddbd"
/> | <img width="400" alt="chevron_project_panel"
src="https://github.com/user-attachments/assets/a626a82e-e5b7-470d-9d93-ed5787dc83d6"
/> | <img width="400" alt="icon_project_panel"
src="https://github.com/user-attachments/assets/20f9c55e-87c4-477a-b4c9-b070d6e5a1db"
/>

### git panel

both | chevron | icon
--- | --- | ---
<img width="400" alt="both_git_panel"
src="https://github.com/user-attachments/assets/3dc166dd-9e63-4943-b803-df3f167876b6"
/> | <img width="400" alt="chevron_git_panel"
src="https://github.com/user-attachments/assets/8dfd2c10-3a68-439a-8019-4951b72e17d1"
/> | <img width="400" alt="icon_git_panel"
src="https://github.com/user-attachments/assets/d78a9938-91e7-4d39-a3c8-04647da67768"
/>

### outline panel

both | chevron | icon
--- | --- | ---
<img width="400" alt="both_outline_panel"
src="https://github.com/user-attachments/assets/1b58c679-0bea-4600-a8ac-e800b0e8d24c"
/> | <img width="400" alt="chevron_outline_panel"
src="https://github.com/user-attachments/assets/0a9358e4-ec89-40d8-8d5e-a53b784ed30a"
/> | <img width="400" alt="icon_outline_panel"
src="https://github.com/user-attachments/assets/d8bf5199-5a8c-4de0-b516-00247e6531a5"
/>



---

Release Notes:

- Added a `folder_indicator` setting that can show the disclosure
chevron and folder icon at the same time in the project, outline, and
git panels.

---------

Co-authored-by: Kirill Bulatov <kirill@zed.dev>

docs/src/migrate/vs-code.md

@@ -155,14 +155,14 @@ The following VS Code settings are automatically imported when you use **Import
 
 **Other**
 
-| VS Code Setting            | Zed Setting                                              |
-| -------------------------- | -------------------------------------------------------- |
-| `http.proxy`               | `proxy`                                                  |
-| `npm.packageManager`       | `node.npm_path`                                          |
-| `telemetry.telemetryLevel` | `telemetry.metrics`, `telemetry.diagnostics`             |
-| `outline.icons`            | `outline_panel.file_icons`, `outline_panel.folder_icons` |
-| `chat.agent.enabled`       | `agent.enabled`                                          |
-| `mcp`                      | `context_servers`                                        |
+| VS Code Setting            | Zed Setting                                                  |
+| -------------------------- | ------------------------------------------------------------ |
+| `http.proxy`               | `proxy`                                                      |
+| `npm.packageManager`       | `node.npm_path`                                              |
+| `telemetry.telemetryLevel` | `telemetry.metrics`, `telemetry.diagnostics`                 |
+| `outline.icons`            | `outline_panel.file_icons`, `outline_panel.folder_indicator` |
+| `chat.agent.enabled`       | `agent.enabled`                                              |
+| `mcp`                      | `context_servers`                                            |
 
 Zed doesn’t import extensions or keybindings, but this import gets core editor behavior close to your VS Code setup. If you skip that step during setup, you can still import settings manually later via the command palette: