Simplify constructing tab content that is purely textual (#14695)

This PR adds a streamlined way to consistently construct tab content for
items that only have textual content in the tabs.

The `Item` trait now has a new `tab_content_text` method that can be
used to return the textual content for the tab.

The `tab_content` method now has a default implementation that—unless
overridden—will construct a `Label` out of the text. This default
implementation also takes care of setting the label color based on the
active state of the tab, something that previously had to be repeated in
each `tab_content` implementation.

The majority of our tabs are now using `tab_content_text`.

Release Notes:

- N/A

crates/markdown_preview/src/markdown_preview_view.rs

@@ -6,13 +6,13 @@ use anyhow::Result;
 use editor::scroll::{Autoscroll, AutoscrollStrategy};
 use editor::{Editor, EditorEvent};
 use gpui::{
-    list, AnyElement, AppContext, ClickEvent, EventEmitter, FocusHandle, FocusableView,
-    InteractiveElement, IntoElement, ListState, ParentElement, Render, Styled, Subscription, Task,
-    View, ViewContext, WeakView,
+    list, AppContext, ClickEvent, EventEmitter, FocusHandle, FocusableView, InteractiveElement,
+    IntoElement, ListState, ParentElement, Render, Styled, Subscription, Task, View, ViewContext,
+    WeakView,
 };
 use language::LanguageRegistry;
 use ui::prelude::*;
-use workspace::item::{Item, ItemHandle, TabContentParams};
+use workspace::item::{Item, ItemHandle};
 use workspace::{Pane, Workspace};
 
 use crate::markdown_elements::ParsedMarkdownElement;
@@ -456,18 +456,12 @@ impl Item for MarkdownPreviewView {
         Some(Icon::new(IconName::FileDoc))
     }
 
-    fn tab_content(&self, params: TabContentParams, _cx: &WindowContext) -> AnyElement {
-        Label::new(if let Some(description) = &self.tab_description {
+    fn tab_content_text(&self, _cx: &WindowContext) -> Option<SharedString> {
+        Some(if let Some(description) = &self.tab_description {
             description.clone().into()
         } else {
             self.fallback_tab_description.clone()
         })
-        .color(if params.selected {
-            Color::Default
-        } else {
-            Color::Muted
-        })
-        .into_any_element()
     }
 
     fn telemetry_event_text(&self) -> Option<&'static str> {