cli: implement better self-updating

- Start separating a "standalone" CLI. This is a little awkward with clap-
  derive, but I got it working. Detection of whether the CLI _is_
  standalone is still todo.
- Remove the old ad-hoc update code for code-server, and use the update
  service instead.
- Fix some of the "permission denied" errors people got while updating
  before. We need to rename the old running binary, not just overwrite it.

cli/src/log.rs

@@ -209,9 +209,9 @@ impl Logger {
 		}
 	}
 
-	pub fn result(&self, message: &str) {
+	pub fn result(&self, message: impl AsRef<str>) {
 		for sink in &self.sink {
-			sink.write_result(message);
+			sink.write_result(message.as_ref());
 		}
 	}