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/window_trait.rs

@@ -9,7 +9,6 @@ use std::rc::Rc;
 
 use euclid::{Length, Scale};
 use servo::compositing::windowing::{EmbedderEvent, WindowMethods};
-use servo::config::opts;
 use servo::embedder_traits::Cursor;
 use servo::servo_geometry::DeviceIndependentPixel;
 use servo::webrender_api::units::{DeviceIntPoint, DeviceIntSize, DevicePixel};
@@ -22,10 +21,7 @@ pub trait WindowPortsMethods: WindowMethods {
     fn id(&self) -> winit::window::WindowId;
     fn hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel> {
         self.device_pixel_ratio_override()
-            .unwrap_or_else(|| match opts::get().output_file {
-                Some(_) => Scale::new(1.0),
-                None => self.device_hidpi_factor(),
-            })
+            .unwrap_or_else(|| self.device_hidpi_factor())
     }
     fn device_hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel>;
     fn device_pixel_ratio_override(