ui2: Reorganize components (#3228)

This PR reorganizes the components in the `ui2` crate.

The distinction between "elements" and "components" is now gone, with
all of the reusable components living under `components/`.

The components that we built while prototyping but will eventually live
in other crates currently reside in the `to_extract/` module.

Release Notes:

- N/A

crates/ui2/src/to_extract/command_palette.rs

@@ -0,0 +1,48 @@
+use crate::prelude::*;
+use crate::{example_editor_actions, OrderMethod, Palette};
+
+#[derive(Component)]
+pub struct CommandPalette {
+    id: ElementId,
+}
+
+impl CommandPalette {
+    pub fn new(id: impl Into<ElementId>) -> Self {
+        Self { id: id.into() }
+    }
+
+    fn render<V: 'static>(self, _view: &mut V, cx: &mut ViewContext<V>) -> impl Component<V> {
+        div().id(self.id.clone()).child(
+            Palette::new("palette")
+                .items(example_editor_actions())
+                .placeholder("Execute a command...")
+                .empty_string("No items found.")
+                .default_order(OrderMethod::Ascending),
+        )
+    }
+}
+
+#[cfg(feature = "stories")]
+pub use stories::*;
+
+#[cfg(feature = "stories")]
+mod stories {
+    use gpui2::{Div, Render};
+
+    use crate::Story;
+
+    use super::*;
+
+    pub struct CommandPaletteStory;
+
+    impl Render for CommandPaletteStory {
+        type Element = Div<Self>;
+
+        fn render(&mut self, cx: &mut ViewContext<Self>) -> Self::Element {
+            Story::container(cx)
+                .child(Story::title_for::<_, CommandPalette>(cx))
+                .child(Story::label(cx, "Default"))
+                .child(CommandPalette::new("command-palette"))
+        }
+    }
+}