Mainline GPUI2 UI work (#3079)

This PR mainlines the current state of new GPUI2-based UI from the
`gpui2-ui` branch.

Release Notes:

- N/A

---------

Co-authored-by: Nate Butler <iamnbutler@gmail.com>
Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>
Co-authored-by: Nate <nate@zed.dev>

crates/storybook/src/storybook.rs

@@ -4,7 +4,7 @@ mod stories;
 mod story;
 mod story_selector;
 
-use std::sync::Arc;
+use std::{process::Command, sync::Arc};
 
 use ::theme as legacy_theme;
 use clap::Parser;
@@ -38,11 +38,44 @@ struct Args {
     theme: Option<String>,
 }
 
+async fn watch_zed_changes(fs: Arc<dyn fs::Fs>) -> Option<()> {
+    if std::env::var("ZED_HOT_RELOAD").is_err() {
+        return None;
+    }
+    use futures::StreamExt;
+    let mut events = fs
+        .watch(".".as_ref(), std::time::Duration::from_millis(100))
+        .await;
+    let mut current_child: Option<std::process::Child> = None;
+    while let Some(events) = events.next().await {
+        if !events.iter().any(|event| {
+            event
+                .path
+                .to_str()
+                .map(|path| path.contains("/crates/"))
+                .unwrap_or_default()
+        }) {
+            continue;
+        }
+        let child = current_child.take().map(|mut child| child.kill());
+        log::info!("Storybook changed, rebuilding...");
+        current_child = Some(
+            Command::new("cargo")
+                .args(["run", "-p", "storybook"])
+                .spawn()
+                .ok()?,
+        );
+    }
+    Some(())
+}
+
 fn main() {
     SimpleLogger::init(LevelFilter::Info, Default::default()).expect("could not initialize logger");
 
     let args = Args::parse();
 
+    let fs = Arc::new(fs::RealFs);
+
     gpui2::App::new(Assets).unwrap().run(move |cx| {
         let mut store = SettingsStore::default();
         store
@@ -63,6 +96,10 @@ fn main() {
             })
             .and_then(|theme_name| theme_registry.get(&theme_name).ok());
 
+        cx.spawn(|_| async move {
+            watch_zed_changes(fs).await;
+        })
+        .detach();
         cx.add_window(
             gpui2::WindowOptions {
                 bounds: WindowBounds::Fixed(RectF::new(vec2f(0., 0.), vec2f(1700., 980.))),