Improve terminal rendering performance (#33345)

Closes #18263

Improvements:

• **Batch text rendering** - Combine adjacent cells with identical
styling into single text runs to reduce draw calls
• **Throttle hyperlink searches** - Limit hyperlink detection to every
100ms or when mouse moves >5px to reduce CPU usage
• **Pre-allocate collections** - Use `Vec::with_capacity()` for cells,
runs, and regions to minimize reallocations
• **Optimize background regions** - Merge adjacent background rectangles
to reduce number of draw operations
• **Cache selection text** - Only compute terminal selection string when
selection exists

Release Notes:

- Improved terminal rendering performance.

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/gpui/src/text_system.rs

@@ -357,6 +357,7 @@ impl WindowTextSystem {
         text: SharedString,
         font_size: Pixels,
         runs: &[TextRun],
+        force_width: Option<Pixels>,
     ) -> ShapedLine {
         debug_assert!(
             text.find('\n').is_none(),
@@ -384,7 +385,7 @@ impl WindowTextSystem {
             });
         }
 
-        let layout = self.layout_line(&text, font_size, runs);
+        let layout = self.layout_line(&text, font_size, runs, force_width);
 
         ShapedLine {
             layout,
@@ -524,6 +525,7 @@ impl WindowTextSystem {
         text: Text,
         font_size: Pixels,
         runs: &[TextRun],
+        force_width: Option<Pixels>,
     ) -> Arc<LineLayout>
     where
         Text: AsRef<str>,
@@ -544,9 +546,9 @@ impl WindowTextSystem {
             });
         }
 
-        let layout = self
-            .line_layout_cache
-            .layout_line(text, font_size, &font_runs);
+        let layout =
+            self.line_layout_cache
+                .layout_line_internal(text, font_size, &font_runs, force_width);
 
         font_runs.clear();
         self.font_runs_pool.lock().push(font_runs);