Add italics and weak to ListItem (#4613)

### What

Add support for italics and weak styling of list items.

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using newly built examples:
[app.rerun.io](https://app.rerun.io/pr/4613/index.html)
* Using examples from latest `main` build:
[app.rerun.io](https://app.rerun.io/pr/4613/index.html?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[app.rerun.io](https://app.rerun.io/pr/4613/index.html?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG

- [PR Build Summary](https://build.rerun.io/pr/4613)
- [Docs
preview](https://rerun.io/preview/2bc097384fff788d1954cb8c65f070d0826348d3/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/2bc097384fff788d1954cb8c65f070d0826348d3/examples)
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- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
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crates/re_ui/src/list_item.rs

@@ -114,6 +114,8 @@ pub struct ListItem<'a> {
     active: bool,
     selected: bool,
     subdued: bool,
+    weak: bool,
+    italics: bool,
     force_hovered: bool,
     collapse_openness: Option<f32>,
     height: f32,
@@ -132,6 +134,8 @@ impl<'a> ListItem<'a> {
             active: true,
             selected: false,
             subdued: false,
+            weak: false,
+            italics: false,
             force_hovered: false,
             collapse_openness: None,
             height: ReUi::list_item_height(),
@@ -166,6 +170,22 @@ impl<'a> ListItem<'a> {
         self
     }
 
+    /// Set the weak state of the item.
+    // TODO(ab): should use design token instead
+    #[inline]
+    pub fn weak(mut self, weak: bool) -> Self {
+        self.weak = weak;
+        self
+    }
+
+    /// Render text in italic.
+    // TODO(ab): should use design token instead
+    #[inline]
+    pub fn italics(mut self, italics: bool) -> Self {
+        self.italics = italics;
+        self
+    }
+
     /// Override the hovered state even if the item is not actually hovered.
     ///
     /// Used to highlight items representing things that are hovered elsewhere in the UI. Note that
@@ -272,7 +292,7 @@ impl<'a> ListItem<'a> {
         }
     }
 
-    fn ui(self, ui: &mut Ui, id: Option<egui::Id>) -> ListItemResponse {
+    fn ui(mut self, ui: &mut Ui, id: Option<egui::Id>) -> ListItemResponse {
         let collapse_extra = if self.collapse_openness.is_some() {
             ReUi::collapsing_triangle_size().x + ReUi::text_to_icon_padding()
         } else {
@@ -284,6 +304,10 @@ impl<'a> ListItem<'a> {
             0.0
         };
 
+        if self.italics {
+            self.text = self.text.italics();
+        }
+
         /// Compute the "ideal" desired width of the item, accounting for text and icon(s) (but not
         /// buttons).
         fn icons_and_label_width(
@@ -342,8 +366,10 @@ impl<'a> ListItem<'a> {
                 ui.visuals().widgets.inactive
             };
 
-            if self.subdued {
-                //TODO(ab): hack, see ['ListItem::subdued']
+            // TODO(ab): use design tokens instead
+            if self.weak {
+                visuals.fg_stroke.color = ui.visuals().weak_text_color();
+            } else if self.subdued {
                 visuals.fg_stroke.color = visuals.fg_stroke.color.gamma_multiply(0.5);
             }