text rendering: support strikethroughs (#7363)

<img width="1269" alt="image"
src="https://github.com/zed-industries/zed/assets/18583882/d4c93033-b2ac-4ae0-8e12-457f256ee869">

Release Notes:

- Added support for styling text with strikethrough.

Related: 
- https://github.com/zed-industries/zed/issues/5364
- https://github.com/zed-industries/zed/pull/7345

crates/gpui/src/text_system/line_wrapper.rs

@@ -225,6 +225,7 @@ mod tests {
                 font: font("Helvetica"),
                 color: Default::default(),
                 underline: Default::default(),
+                strikethrough: None,
                 background_color: None,
             };
             let bold = TextRun {
@@ -232,6 +233,7 @@ mod tests {
                 font: font("Helvetica").bold(),
                 color: Default::default(),
                 underline: Default::default(),
+                strikethrough: None,
                 background_color: None,
             };