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/ui/src/components/label/highlighted_label.rs

@@ -43,6 +43,11 @@ impl LabelCommon for HighlightedLabel {
         self.base = self.base.strikethrough(strikethrough);
         self
     }
+
+    fn italic(mut self, italic: bool) -> Self {
+        self.base = self.base.italic(italic);
+        self
+    }
 }
 
 impl RenderOnce for HighlightedLabel {

crates/ui/src/components/label/label.rs

@@ -126,6 +126,20 @@ impl LabelCommon for Label {
         self.base = self.base.strikethrough(strikethrough);
         self
     }
+
+    /// Sets the italic property of the label.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use ui::prelude::*;
+    ///
+    /// let my_label = Label::new("Hello, World!").italic(true);
+    /// ```
+    fn italic(mut self, italic: bool) -> Self {
+        self.base = self.base.italic(italic);
+        self
+    }
 }
 
 impl RenderOnce for Label {

crates/ui/src/components/label/label_like.rs

@@ -33,6 +33,9 @@ pub trait LabelCommon {
 
     /// Sets the strikethrough property of the label.
     fn strikethrough(self, strikethrough: bool) -> Self;
+
+    /// Sets the italic property of the label.
+    fn italic(self, italic: bool) -> Self;
 }
 
 #[derive(IntoElement)]
@@ -41,6 +44,7 @@ pub struct LabelLike {
     line_height_style: LineHeightStyle,
     pub(crate) color: Color,
     strikethrough: bool,
+    italic: bool,
     children: SmallVec<[AnyElement; 2]>,
 }
 
@@ -51,6 +55,7 @@ impl LabelLike {
             line_height_style: LineHeightStyle::default(),
             color: Color::Default,
             strikethrough: false,
+            italic: false,
             children: SmallVec::new(),
         }
     }
@@ -76,6 +81,11 @@ impl LabelCommon for LabelLike {
         self.strikethrough = strikethrough;
         self
     }
+
+    fn italic(mut self, italic: bool) -> Self {
+        self.italic = italic;
+        self
+    }
 }
 
 impl ParentElement for LabelLike {
@@ -106,6 +116,7 @@ impl RenderOnce for LabelLike {
             .when(self.line_height_style == LineHeightStyle::UiLabel, |this| {
                 this.line_height(relative(1.))
             })
+            .when(self.italic, |this| this.italic())
             .text_color(self.color.color(cx))
             .children(self.children)
     }