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/editor/src/items.rs

@@ -19,7 +19,7 @@ use project::repository::GitFileStatus;
 use project::{search::SearchQuery, FormatTrigger, Item as _, Project, ProjectPath};
 use rpc::proto::{self, update_view, PeerId};
 use settings::Settings;
-use workspace::item::ItemSettings;
+use workspace::item::{ItemSettings, TabContentParams};
 
 use std::{
     borrow::Cow,
@@ -594,7 +594,7 @@ impl Item for Editor {
         Some(path.to_string_lossy().to_string().into())
     }
 
-    fn tab_content(&self, detail: Option<usize>, selected: bool, cx: &WindowContext) -> AnyElement {
+    fn tab_content(&self, params: TabContentParams, cx: &WindowContext) -> AnyElement {
         let label_color = if ItemSettings::get_global(cx).git_status {
             self.buffer()
                 .read(cx)
@@ -602,14 +602,14 @@ impl Item for Editor {
                 .and_then(|buffer| buffer.read(cx).project_path(cx))
                 .and_then(|path| self.project.as_ref()?.read(cx).entry_for_path(&path, cx))
                 .map(|entry| {
-                    entry_git_aware_label_color(entry.git_status, entry.is_ignored, selected)
+                    entry_git_aware_label_color(entry.git_status, entry.is_ignored, params.selected)
                 })
-                .unwrap_or_else(|| entry_label_color(selected))
+                .unwrap_or_else(|| entry_label_color(params.selected))
         } else {
-            entry_label_color(selected)
+            entry_label_color(params.selected)
         };
 
-        let description = detail.and_then(|detail| {
+        let description = params.detail.and_then(|detail| {
             let path = path_for_buffer(&self.buffer, detail, false, cx)?;
             let description = path.to_string_lossy();
             let description = description.trim();
@@ -623,7 +623,11 @@ impl Item for Editor {
 
         h_flex()
             .gap_2()
-            .child(Label::new(self.title(cx).to_string()).color(label_color))
+            .child(
+                Label::new(self.title(cx).to_string())
+                    .color(label_color)
+                    .italic(params.preview),
+            )
             .when_some(description, |this, description| {
                 this.child(
                     Label::new(description)