api: Flatten and simplify Servo preferences (#34966)

Flatten and simplify Servo's preferences code. In addition, have both
preferences and options passed in as arguments to `Servo::new()` and
make sure not to use the globally set preferences in `servoshell` (as
much as possible now).

Instead of a complex procedural macro to generate preferences, just
expose a very simple derive macro that adds string based getters and
setters.

- All command-line parsing is moved to servoshell.
- There is no longer the concept of a missing preference.
- Preferences no longer have to be part of the resources bundle because
  they now have reasonable default values.
- servoshell specific preferences are no longer part of the preferences
  exposed by the Servo API.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/serviceworkerglobalscope.rs

@@ -306,7 +306,7 @@ impl ServiceWorkerGlobalScope {
 
                 // Service workers are time limited
                 // https://w3c.github.io/ServiceWorker/#service-worker-lifetime
-                let sw_lifetime_timeout = pref!(dom.serviceworker.timeout_seconds) as u64;
+                let sw_lifetime_timeout = pref!(dom_serviceworker_timeout_seconds) as u64;
                 let time_out_port = after(Duration::new(sw_lifetime_timeout, 0));
 
                 let (devtools_mpsc_chan, devtools_mpsc_port) = unbounded();