Remove checked-in theme JSON files

* Generate the themes on build
* In debug builds, watch the theme sources. When they change, re-generate
  the themes and reload the current theme, removing the need for the
  `theme_selector::Reload` command.

Co-authored-by: Keith Simmons <keith@zed.dev>

crates/zed/build.rs

@@ -1,3 +1,31 @@
+use std::process::Command;
+
 fn main() {
     println!("cargo:rustc-env=MACOSX_DEPLOYMENT_TARGET=10.14");
+
+    let output = Command::new("npm")
+        .current_dir("../../styles")
+        .args(["ci"])
+        .output()
+        .expect("failed to run npm");
+    if !output.status.success() {
+        panic!(
+            "failed to install theme dependencies {}",
+            String::from_utf8_lossy(&output.stderr)
+        );
+    }
+
+    let output = Command::new("npm")
+        .current_dir("../../styles")
+        .args(["run", "build-themes"])
+        .output()
+        .expect("failed to run npm");
+    if !output.status.success() {
+        panic!(
+            "build-themes script failed {}",
+            String::from_utf8_lossy(&output.stderr)
+        );
+    }
+
+    println!("cargo:rerun-if-changed=../../styles");
 }