Add preview tabs (#9125)

This PR implements the preview tabs feature from VSCode.
More details and thanks for the head start of the implementation here
#6782.

Here is what I have observed from using the vscode implementation ([x]
-> already implemented):
- [x] Single click on project file opens tab as preview
- [x] Double click on item in project panel opens tab as permanent
- [x] Double click on the tab makes it permanent
- [x] Navigating away from the tab makes the tab permanent and the new
tab is shown as preview (e.g. GoToReference)
- [x] Existing preview tab is reused when opening a new tab
- [x] Dragging tab to the same/another panel makes the tab permanent
- [x] Opening a tab from the file finder makes the tab permanent
- [x] Editing a preview tab will make the tab permanent
- [x] Using the space key in the project panel opens the tab as preview
- [x] Handle navigation history correctly (restore a preview tab as
preview as well)
- [x] Restore preview tabs after restarting
- [x] Support opening files from file finder in preview mode (vscode:
"Enable Preview From Quick Open")
 
I need to do some more testing of the vscode implementation, there might
be other behaviors/workflows which im not aware of that open an item as
preview/make them permanent.

Showcase:


https://github.com/zed-industries/zed/assets/53836821/9be16515-c740-4905-bea1-88871112ef86


TODOs
- [x] Provide `enable_preview_tabs` setting
- [x] Write some tests
- [x] How should we handle this in collaboration mode (have not tested
the behavior so far)
- [x] Keyboard driven usage (probably need workspace commands)
- [x] Register `TogglePreviewTab` only when setting enabled?
- [x] Render preview tabs in tab switcher as italic
- [x] Render preview tabs in image viewer as italic
- [x] Should this be enabled by default (it is the default behavior in
VSCode)?
- [x] Docs

Future improvements (out of scope for now):
- Support preview mode for find all references and possibly other
multibuffers (VSCode: "Enable Preview From Code Navigation")


Release Notes:

- Added preview tabs
([#4922](https://github.com/zed-industries/zed/issues/4922)).

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/tab_switcher/src/tab_switcher.rs

@@ -13,7 +13,7 @@ use std::sync::Arc;
 use ui::{prelude::*, ListItem, ListItemSpacing, Tooltip};
 use util::ResultExt;
 use workspace::{
-    item::ItemHandle,
+    item::{ItemHandle, TabContentParams},
     pane::{render_item_indicator, tab_details, Event as PaneEvent},
     ModalView, Pane, SaveIntent, Workspace,
 };
@@ -130,6 +130,7 @@ struct TabMatch {
     item_index: usize,
     item: Box<dyn ItemHandle>,
     detail: usize,
+    preview: bool,
 }
 
 pub struct TabSwitcherDelegate {
@@ -202,6 +203,7 @@ impl TabSwitcherDelegate {
                 item_index,
                 item: item.boxed_clone(),
                 detail,
+                preview: pane.is_active_preview_item(item.item_id()),
             })
             .for_each(|tab_match| self.matches.push(tab_match));
 
@@ -324,7 +326,12 @@ impl PickerDelegate for TabSwitcherDelegate {
             .get(ix)
             .expect("Invalid matches state: no element for index {ix}");
 
-        let label = tab_match.item.tab_content(Some(tab_match.detail), true, cx);
+        let params = TabContentParams {
+            detail: Some(tab_match.detail),
+            selected: true,
+            preview: tab_match.preview,
+        };
+        let label = tab_match.item.tab_content(params, cx);
         let indicator = render_item_indicator(tab_match.item.boxed_clone(), cx);
         let indicator_color = if let Some(ref indicator) = indicator {
             indicator.color