Restructure ui into just elements and components (#3023)

This PR restructures the `ui` crate into just `elements` and
`components`.

This was already done on the `gpui2-ui` branch, just getting it onto
`main`.

Release Notes:

- N/A

---------

Co-authored-by: Nate Butler <nate@zed.dev>

crates/ui/src/components/command_palette.rs

@@ -0,0 +1,31 @@
+use gpui2::elements::div;
+use gpui2::{elements::div::ScrollState, ViewContext};
+use gpui2::{Element, IntoElement, ParentElement};
+use std::marker::PhantomData;
+
+use crate::{example_editor_actions, palette, OrderMethod};
+
+#[derive(Element)]
+pub struct CommandPalette<V: 'static> {
+    view_type: PhantomData<V>,
+    scroll_state: ScrollState,
+}
+
+pub fn command_palette<V: 'static>(scroll_state: ScrollState) -> CommandPalette<V> {
+    CommandPalette {
+        view_type: PhantomData,
+        scroll_state,
+    }
+}
+
+impl<V: 'static> CommandPalette<V> {
+    fn render(&mut self, _: &mut V, cx: &mut ViewContext<V>) -> impl IntoElement<V> {
+        div().child(
+            palette(self.scroll_state.clone())
+                .items(example_editor_actions())
+                .placeholder("Execute a command...")
+                .empty_string("No items found.")
+                .default_order(OrderMethod::Ascending),
+        )
+    }
+}