Add letter spacing and text transforms to GPUI (#111)

* Add text spacing and transform style plumbing

* Apply byte-stable transforms and spacing-aware truncation

* Add platform letter spacing support

* Fix scheduler clippy warning

* Refresh dependency lockfile

* Fix CI for text spacing changes

* Add text transform preview example

crates/gpui_elements/src/editable_text/element.rs

@@ -585,6 +585,7 @@ impl PrelayoutState {
                     background_color: None,
                     underline: None,
                     strikethrough: None,
+                    letter_spacing: None,
                 }];
 
                 let wrap_width = TextLayout::evaluate_wrap_width(