Remove editor instances concept and clean up JS interop code

editor/src/application.rs

@@ -9,7 +9,7 @@ pub struct Editor {
 }
 
 impl Editor {
-	/// Construct a new editor instance.
+	/// Construct the editor.
 	/// Remember to provide a random seed with `editor::set_uuid_seed(seed)` before any editors can be used.
 	pub fn new() -> Self {
 		Self { dispatcher: Dispatcher::new() }

editor/src/dispatcher.rs

@@ -273,7 +273,7 @@ mod test {
 		let _ = env_logger::builder().is_test(true).try_init();
 	}
 
-	/// Create an editor instance with three layers
+	/// Create an editor with three layers
 	/// 1. A red rectangle
 	/// 2. A blue shape
 	/// 3. A green ellipse