Rename fields in ThemeColors (#3242)

This PR applies a number of field renames in the `ThemeColors` struct
from the `import-theme` branch.

This will help prevent this branch from diverging too far from `main`.

Release Notes:

- N/A

---------

Co-authored-by: Nate Butler <iamnbutler@gmail.com>
Co-authored-by: Marshall Bowers <1486634+maxdeviant@users.noreply.github.com>

crates/ui2/src/components/context_menu.rs

@@ -46,7 +46,7 @@ impl ContextMenu {
     fn render<V: 'static>(self, _view: &mut V, cx: &mut ViewContext<V>) -> impl Component<V> {
         v_stack()
             .flex()
-            .bg(cx.theme().colors().elevated_surface)
+            .bg(cx.theme().colors().elevated_surface_background)
             .border()
             .border_color(cx.theme().colors().border)
             .child(List::new(