Add support for excluding files based on .gitignore (#26636)

Closes: #17543

Release Notes:

- **New Feature:** Introduced the ability to automatically remove files
and directories from the Zed project panel that are specified in
`.gitignore`.
- **Configuration Option:** This behavior can be controlled via the new
`project_panel.hide_gitignore` setting. By setting it to `true`, files
listed in `.gitignore` will be excluded from the project panel.
- **Toggle:** Ability to toggle this setting using the action
`ProjectPanel::ToggleHideGitIgnore`

```json
  "project_panel": {
    "hide_gitignore": true
  },

```

This results in a cleaner and easier to browse project panel for
projects that generate a lot of object files like `xv6-riscv` or `linux`
without needing to tweak `file_scan_exclusions` on `settings.json`

**Preview:**
- With `"project_panel.hide_gitignore": false` (default, this is how zed
currently looks)

![Screenshot From 2025-03-23
12-50-17](https://github.com/user-attachments/assets/15607e73-a474-4188-982a-eed4e0551061)

- With `"project_panel.hide_gitignore": true` 

![Screenshot From 2025-03-23
12-50-27](https://github.com/user-attachments/assets/3e281f92-294c-4133-b5e3-25e17f15bd4d)

- Action `ProjectPanel::ToggleHideGitIgnore`

![Screenshot From 2025-03-23
12-50-55](https://github.com/user-attachments/assets/4d03db33-75ad-471c-814c-098698a8cb38)

crates/project_panel/src/project_panel_settings.rs

@@ -31,6 +31,7 @@ pub enum EntrySpacing {
 #[derive(Deserialize, Debug, Clone, Copy, PartialEq)]
 pub struct ProjectPanelSettings {
     pub button: bool,
+    pub hide_gitignore: bool,
     pub default_width: Pixels,
     pub dock: ProjectPanelDockPosition,
     pub entry_spacing: EntrySpacing,
@@ -93,6 +94,10 @@ pub struct ProjectPanelSettingsContent {
     ///
     /// Default: true
     pub button: Option<bool>,
+    /// Whether to hide gitignore files in the project panel.
+    ///
+    /// Default: false
+    pub hide_gitignore: Option<bool>,
     /// Customize default width (in pixels) taken by project panel
     ///
     /// Default: 240