gpui: Fix line_through, underline position when used text center or right (#24721)

Release Notes:

- N/A

---

| Before | After |
| --- | --- |
| <img width="912" alt="image"
src="https://github.com/user-attachments/assets/0640ac85-ee5d-4707-b866-997e36608c18"
/> | <img width="912" alt="image"
src="https://github.com/user-attachments/assets/caf84477-a7bc-4c22-a9e6-f44c3b6f86ef"
/> |
 
And fix the `line_through` doc link.

crates/gpui/src/text_system/line.rs

@@ -355,7 +355,7 @@ fn paint_line(
             }
         }
 
-        let mut last_line_end_x = origin.x + layout.width;
+        let mut last_line_end_x = glyph_origin.x;
         if let Some(boundary) = wrap_boundaries.last() {
             let run = &layout.runs[boundary.run_ix];
             let glyph = &run.glyphs[boundary.glyph_ix];