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/ui/src/components/tooltip.rs

@@ -96,7 +96,7 @@ pub fn tooltip_container<V>(
         v_flex()
             .elevation_2(cx)
             .font_family(ui_font)
-            .text_ui()
+            .text_ui(cx)
             .text_color(cx.theme().colors().text)
             .py_1()
             .px_2()