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/components/assistant_panel.rs

@@ -1,93 +0,0 @@
-use crate::prelude::*;
-use crate::{Icon, IconButton, Label, Panel, PanelSide};
-use gpui2::{rems, AbsoluteLength};
-
-#[derive(Component)]
-pub struct AssistantPanel {
-    id: ElementId,
-    current_side: PanelSide,
-}
-
-impl AssistantPanel {
-    pub fn new(id: impl Into<ElementId>) -> Self {
-        Self {
-            id: id.into(),
-            current_side: PanelSide::default(),
-        }
-    }
-
-    pub fn side(mut self, side: PanelSide) -> Self {
-        self.current_side = side;
-        self
-    }
-
-    fn render<V: 'static>(self, view: &mut V, cx: &mut ViewContext<V>) -> impl Component<V> {
-        Panel::new(self.id.clone(), cx)
-            .children(vec![div()
-                .flex()
-                .flex_col()
-                .h_full()
-                .px_2()
-                .gap_2()
-                // Header
-                .child(
-                    div()
-                        .flex()
-                        .justify_between()
-                        .gap_2()
-                        .child(
-                            div()
-                                .flex()
-                                .child(IconButton::new("menu", Icon::Menu))
-                                .child(Label::new("New Conversation")),
-                        )
-                        .child(
-                            div()
-                                .flex()
-                                .items_center()
-                                .gap_px()
-                                .child(IconButton::new("split_message", Icon::SplitMessage))
-                                .child(IconButton::new("quote", Icon::Quote))
-                                .child(IconButton::new("magic_wand", Icon::MagicWand))
-                                .child(IconButton::new("plus", Icon::Plus))
-                                .child(IconButton::new("maximize", Icon::Maximize)),
-                        ),
-                )
-                // Chat Body
-                .child(
-                    div()
-                        .id("chat-body")
-                        .w_full()
-                        .flex()
-                        .flex_col()
-                        .gap_3()
-                        .overflow_y_scroll()
-                        .child(Label::new("Is this thing on?")),
-                )
-                .render()])
-            .side(self.current_side)
-            .width(AbsoluteLength::Rems(rems(32.)))
-    }
-}
-
-#[cfg(feature = "stories")]
-pub use stories::*;
-
-#[cfg(feature = "stories")]
-mod stories {
-    use super::*;
-    use crate::Story;
-    use gpui2::{Div, Render};
-    pub struct AssistantPanelStory;
-
-    impl Render for AssistantPanelStory {
-        type Element = Div<Self>;
-
-        fn render(&mut self, cx: &mut ViewContext<Self>) -> Self::Element {
-            Story::container(cx)
-                .child(Story::title_for::<_, AssistantPanel>(cx))
-                .child(Story::label(cx, "Default"))
-                .child(AssistantPanel::new("assistant-panel"))
-        }
-    }
-}