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/chat_panel.rs

@@ -0,0 +1,66 @@
+use std::marker::PhantomData;
+
+use gpui2::elements::div::ScrollState;
+use gpui2::style::StyleHelpers;
+use gpui2::{elements::div, IntoElement};
+use gpui2::{Element, ParentElement, ViewContext};
+
+use crate::theme::theme;
+use crate::{icon_button, IconAsset};
+
+#[derive(Element)]
+pub struct ChatPanel<V: 'static> {
+    view_type: PhantomData<V>,
+    scroll_state: ScrollState,
+}
+
+pub fn chat_panel<V: 'static>(scroll_state: ScrollState) -> ChatPanel<V> {
+    ChatPanel {
+        view_type: PhantomData,
+        scroll_state,
+    }
+}
+
+impl<V: 'static> ChatPanel<V> {
+    fn render(&mut self, _: &mut V, cx: &mut ViewContext<V>) -> impl IntoElement<V> {
+        let theme = theme(cx);
+
+        div()
+            .h_full()
+            .flex()
+            // Header
+            .child(
+                div()
+                    .px_2()
+                    .flex()
+                    .gap_2()
+                    // Nav Buttons
+                    .child("#gpui2"),
+            )
+            // Chat Body
+            .child(
+                div()
+                    .w_full()
+                    .flex()
+                    .flex_col()
+                    .overflow_y_scroll(self.scroll_state.clone())
+                    .child("body"),
+            )
+            // Composer
+            .child(
+                div()
+                    .px_2()
+                    .flex()
+                    .gap_2()
+                    // Nav Buttons
+                    .child(
+                        div()
+                            .flex()
+                            .items_center()
+                            .gap_px()
+                            .child(icon_button().icon(IconAsset::Plus))
+                            .child(icon_button().icon(IconAsset::Split)),
+                    ),
+            )
+    }
+}