Add window::Settings::fullscreen

Corresponds to `winit::window::WindowAttributes::with_fullscreen`.

Currently only allows to set `Fullscreen::Borderless(None)` meaning
borderless on the current monitor, exclusive fullscreen does not
make sense for a GUI and iced does not expose monitors yet.

core/src/window/settings.rs

@@ -37,6 +37,9 @@ pub struct Settings {
     /// Whether the window should start maximized.
     pub maximized: bool,
 
+    /// Whether the window should start fullscreen.
+    pub fullscreen: bool,
+
     /// The initial position of the window.
     pub position: Position,
 
@@ -83,6 +86,7 @@ impl Default for Settings {
         Self {
             size: Size::new(1024.0, 768.0),
             maximized: false,
+            fullscreen: false,
             position: Position::default(),
             min_size: None,
             max_size: None,

winit/src/conversion.rs

@@ -24,6 +24,11 @@ pub fn window_attributes(
             height: settings.size.height,
         })
         .with_maximized(settings.maximized)
+        .with_fullscreen(
+            settings
+                .fullscreen
+                .then_some(winit::window::Fullscreen::Borderless(None)),
+        )
         .with_resizable(settings.resizable)
         .with_enabled_buttons(if settings.resizable {
             winit::window::WindowButtons::all()