Break typography styles out of StyledExt (#11013)

- Centralizes typography-related UI styles and methods in
`styles/typography.rs`
- Breaks the typography-related styles out of `StyledExt`. This means we
add a `StyledTypography` trait – this should more or less be an
invisible change as we publish it in the prelude.
- adds the ability to easily grab the UI or Buffer font sizes
(`ui_font_size`, `buffer_font_size`) with `TextSize::UI`,
`TextSize::Editor`

Release Notes:

- N/A

crates/breadcrumbs/src/breadcrumbs.rs

@@ -33,7 +33,7 @@ impl EventEmitter<ToolbarItemEvent> for Breadcrumbs {}
 impl Render for Breadcrumbs {
     fn render(&mut self, cx: &mut ViewContext<Self>) -> impl IntoElement {
         const MAX_SEGMENTS: usize = 12;
-        let element = h_flex().text_ui();
+        let element = h_flex().text_ui(cx);
         let Some(active_item) = self.active_item.as_ref() else {
             return element;
         };