WIP: Allow specifying font features in the editor

This just lays the foundation for threading through a `fonts::Features`
struct, but it's not used yet.

crates/gpui/src/elements/label.rs

@@ -216,6 +216,7 @@ mod tests {
             12.,
             Default::default(),
             Default::default(),
+            Default::default(),
             Color::black(),
             cx.font_cache(),
         )
@@ -225,6 +226,7 @@ mod tests {
             12.,
             *FontProperties::new().weight(Weight::BOLD),
             Default::default(),
+            Default::default(),
             Color::new(255, 0, 0, 255),
             cx.font_cache(),
         )