Mainline GPUI2 UI work (#3062)

This PR mainlines the current state of new GPUI2-based UI from the
`gpui2-ui` branch.

Release Notes:

- N/A

---------

Co-authored-by: Nate Butler <iamnbutler@gmail.com>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Marshall Bowers <1486634+maxdeviant@users.noreply.github.com>
Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>
Co-authored-by: Nate <nate@zed.dev>
Co-authored-by: Mikayla <mikayla@zed.dev>

crates/storybook/src/stories/components/context_menu.rs

@@ -0,0 +1,21 @@
+use ui::prelude::*;
+use ui::{ContextMenu, ContextMenuItem, Label};
+
+use crate::story::Story;
+
+#[derive(Element, Default)]
+pub struct ContextMenuStory {}
+
+impl ContextMenuStory {
+    fn render<V: 'static>(&mut self, _: &mut V, cx: &mut ViewContext<V>) -> impl IntoElement<V> {
+        Story::container(cx)
+            //.fill(theme.middle.base.default.background)
+            .child(Story::title_for::<_, ContextMenu>(cx))
+            .child(Story::label(cx, "Default"))
+            .child(ContextMenu::new([
+                ContextMenuItem::header("Section header"),
+                ContextMenuItem::Separator,
+                ContextMenuItem::entry(Label::new("Some entry")),
+            ]))
+    }
+}