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/label/label_like.rs

@@ -108,10 +108,10 @@ impl RenderOnce for LabelLike {
                 )
             })
             .map(|this| match self.size {
-                LabelSize::Large => this.text_ui_lg(),
-                LabelSize::Default => this.text_ui(),
-                LabelSize::Small => this.text_ui_sm(),
-                LabelSize::XSmall => this.text_ui_xs(),
+                LabelSize::Large => this.text_ui_lg(cx),
+                LabelSize::Default => this.text_ui(cx),
+                LabelSize::Small => this.text_ui_sm(cx),
+                LabelSize::XSmall => this.text_ui_xs(cx),
             })
             .when(self.line_height_style == LineHeightStyle::UiLabel, |this| {
                 this.line_height(relative(1.))