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/servoparser/mod.rs

@@ -158,7 +158,7 @@ impl ServoParser {
         url: ServoUrl,
         can_gc: CanGc,
     ) {
-        let parser = if pref!(dom.servoparser.async_html_tokenizer.enabled) {
+        let parser = if pref!(dom_servoparser_async_html_tokenizer_enabled) {
             ServoParser::new(
                 document,
                 Tokenizer::AsyncHtml(self::async_html::Tokenizer::new(document, url, None)),