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/list.rs

@@ -0,0 +1,64 @@
+use crate::theme::theme;
+use crate::tokens::token;
+use crate::{icon, label, prelude::*, IconAsset, LabelColor, ListItem, ListSectionHeader};
+use gpui2::style::StyleHelpers;
+use gpui2::{elements::div, IntoElement};
+use gpui2::{Element, ParentElement, ViewContext};
+
+#[derive(Element)]
+pub struct List {
+    header: Option<ListSectionHeader>,
+    items: Vec<ListItem>,
+    empty_message: &'static str,
+    toggle: Option<ToggleState>,
+    // footer: Option<ListSectionFooter>,
+}
+
+pub fn list(items: Vec<ListItem>) -> List {
+    List {
+        header: None,
+        items,
+        empty_message: "No items",
+        toggle: None,
+    }
+}
+
+impl List {
+    pub fn header(mut self, header: ListSectionHeader) -> Self {
+        self.header = Some(header);
+        self
+    }
+
+    pub fn empty_message(mut self, empty_message: &'static str) -> Self {
+        self.empty_message = empty_message;
+        self
+    }
+
+    pub fn set_toggle(mut self, toggle: ToggleState) -> Self {
+        self.toggle = Some(toggle);
+        self
+    }
+
+    fn render<V: 'static>(&mut self, _: &mut V, cx: &mut ViewContext<V>) -> impl IntoElement<V> {
+        let theme = theme(cx);
+        let token = token();
+
+        let disclosure_control = match self.toggle {
+            Some(ToggleState::NotToggled) => Some(icon(IconAsset::ChevronRight)),
+            Some(ToggleState::Toggled) => Some(icon(IconAsset::ChevronDown)),
+            None => None,
+        };
+
+        div()
+            .py_1()
+            .flex()
+            .flex_col()
+            .children(self.header.map(|h| h))
+            .children(
+                self.items
+                    .is_empty()
+                    .then(|| label(self.empty_message).color(LabelColor::Muted)),
+            )
+            .children(self.items.iter().cloned())
+    }
+}