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>

ports/servoshell/desktop/headless_window.rs

@@ -13,7 +13,6 @@ use euclid::{Box2D, Length, Point2D, Scale, Size2D};
 use servo::compositing::windowing::{
     AnimationState, EmbedderCoordinates, EmbedderEvent, WindowMethods,
 };
-use servo::config::opts;
 use servo::servo_geometry::DeviceIndependentPixel;
 use servo::webrender_api::units::{DeviceIntSize, DevicePixel};
 
@@ -34,6 +33,7 @@ impl Window {
     pub fn new(
         size: Size2D<u32, DeviceIndependentPixel>,
         device_pixel_ratio_override: Option<f32>,
+        screen_size_override: Option<Size2D<u32, DeviceIndependentPixel>>,
     ) -> Rc<dyn WindowPortsMethods> {
         let device_pixel_ratio_override: Option<Scale<f32, DeviceIndependentPixel, DevicePixel>> =
             device_pixel_ratio_override.map(Scale::new);
@@ -43,7 +43,7 @@ impl Window {
         let inner_size = Cell::new((size.to_f32() * hidpi_factor).to_i32());
         let window_rect = Box2D::from_origin_and_size(Point2D::zero(), size);
 
-        let screen_size = opts::get().screen_size_override.map_or_else(
+        let screen_size = screen_size_override.map_or_else(
             || window_rect.size(),
             |screen_size_override| screen_size_override.to_i32(),
         );