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/buffer_search.rs

@@ -0,0 +1,43 @@
+use gpui2::{Div, Render, View, VisualContext};
+
+use crate::prelude::*;
+use crate::{h_stack, Icon, IconButton, IconColor, Input};
+
+#[derive(Clone)]
+pub struct BufferSearch {
+    is_replace_open: bool,
+}
+
+impl BufferSearch {
+    pub fn new() -> Self {
+        Self {
+            is_replace_open: false,
+        }
+    }
+
+    fn toggle_replace(&mut self, cx: &mut ViewContext<Self>) {
+        self.is_replace_open = !self.is_replace_open;
+
+        cx.notify();
+    }
+
+    pub fn view(cx: &mut WindowContext) -> View<Self> {
+        cx.build_view(|cx| Self::new())
+    }
+}
+
+impl Render for BufferSearch {
+    type Element = Div<Self>;
+
+    fn render(&mut self, cx: &mut ViewContext<Self>) -> Div<Self> {
+        h_stack().bg(cx.theme().colors().toolbar).p_2().child(
+            h_stack().child(Input::new("Search")).child(
+                IconButton::<Self>::new("replace", Icon::Replace)
+                    .when(self.is_replace_open, |this| this.color(IconColor::Accent))
+                    .on_click(|buffer_search, cx| {
+                        buffer_search.toggle_replace(cx);
+                    }),
+            ),
+        )
+    }
+}