editor: Improve text color in document color highlight (#39372)

Release Notes:

- Improved text color in LSP document color highlight.

----

Because highlight ranges are implemented using a paint background,
there's no way to control the text color.

I've been thinking about this problem for a long time, want to solve it.

~~Today, I come up with a new idea. Re-rendering the document color text
at the top should solve this problem.~~

#### Update 10/6: 

> The previous version is not good, when we have soft wrap text, that
version will not work correct.

Now use exists `bg_segments_per_row` feature to fix text color.

## Before

<img width="563" height="540" alt="image"
src="https://github.com/user-attachments/assets/99722253-0cab-4d2a-a5d1-7f28393bcaed"
/>


## After

<img width="544" height="527" alt="image"
src="https://github.com/user-attachments/assets/a1bf6cdb-0e9c-435d-b14a-6ee9159a63d9"
/>

crates/editor/src/element.rs

@@ -8931,10 +8931,20 @@ impl Element for EditorElement {
                         cx,
                     );
 
+                    let merged_highlighted_ranges =
+                        if let Some((_, colors)) = document_colors.as_ref() {
+                            &highlighted_ranges
+                                .clone()
+                                .into_iter()
+                                .chain(colors.clone())
+                                .collect()
+                        } else {
+                            &highlighted_ranges
+                        };
                     let bg_segments_per_row = Self::bg_segments_per_row(
                         start_row..end_row,
                         &selections,
-                        &highlighted_ranges,
+                        &merged_highlighted_ranges,
                         self.style.background,
                     );