Factor out LabelLike to share common label styles (#3510)

This PR factors out a new `LabelLike` component to share common styles
between the `Label` and `HighlightedLabel` components.

Release Notes:

- N/A

crates/ui2/src/components/label/highlighted_label.rs

@@ -0,0 +1,86 @@
+use std::ops::Range;
+
+use gpui::{HighlightStyle, StyledText};
+
+use crate::{prelude::*, LabelCommon, LabelLike, LabelSize, LineHeightStyle};
+
+#[derive(IntoElement)]
+pub struct HighlightedLabel {
+    base: LabelLike,
+    label: SharedString,
+    highlight_indices: Vec<usize>,
+}
+
+impl HighlightedLabel {
+    /// Constructs a label with the given characters highlighted.
+    /// Characters are identified by UTF-8 byte position.
+    pub fn new(label: impl Into<SharedString>, highlight_indices: Vec<usize>) -> Self {
+        Self {
+            base: LabelLike::new(),
+            label: label.into(),
+            highlight_indices,
+        }
+    }
+}
+
+impl LabelCommon for HighlightedLabel {
+    fn size(mut self, size: LabelSize) -> Self {
+        self.base = self.base.size(size);
+        self
+    }
+
+    fn line_height_style(mut self, line_height_style: LineHeightStyle) -> Self {
+        self.base = self.base.line_height_style(line_height_style);
+        self
+    }
+
+    fn color(mut self, color: Color) -> Self {
+        self.base = self.base.color(color);
+        self
+    }
+
+    fn strikethrough(mut self, strikethrough: bool) -> Self {
+        self.base = self.base.strikethrough(strikethrough);
+        self
+    }
+}
+
+impl RenderOnce for HighlightedLabel {
+    type Rendered = LabelLike;
+
+    fn render(self, cx: &mut WindowContext) -> Self::Rendered {
+        let highlight_color = cx.theme().colors().text_accent;
+
+        let mut highlight_indices = self.highlight_indices.iter().copied().peekable();
+        let mut highlights: Vec<(Range<usize>, HighlightStyle)> = Vec::new();
+
+        while let Some(start_ix) = highlight_indices.next() {
+            let mut end_ix = start_ix;
+
+            loop {
+                end_ix = end_ix + self.label[end_ix..].chars().next().unwrap().len_utf8();
+                if let Some(&next_ix) = highlight_indices.peek() {
+                    if next_ix == end_ix {
+                        end_ix = next_ix;
+                        highlight_indices.next();
+                        continue;
+                    }
+                }
+                break;
+            }
+
+            highlights.push((
+                start_ix..end_ix,
+                HighlightStyle {
+                    color: Some(highlight_color),
+                    ..Default::default()
+                },
+            ));
+        }
+
+        let mut text_style = cx.text_style().clone();
+        text_style.color = self.base.color.color(cx);
+
+        LabelLike::new().child(StyledText::new(self.label).with_highlights(&text_style, highlights))
+    }
+}