Web: return MonitorHandle in Window::fullscreen() (#3861)

- Change `OrientationData::natural` type from `bool` to `Orientation`, just telling the user what the natural orientation is.
- Fix and improve some monitor related documentation.

src/platform_impl/web/monitor.rs

@@ -322,22 +322,22 @@ impl Inner {
             OrientationType::LandscapePrimary => OrientationData {
                 orientation: Orientation::Landscape,
                 flipped: false,
-                natural: angle == 0,
+                natural: if angle == 0 { Orientation::Landscape } else { Orientation::Portrait },
             },
             OrientationType::LandscapeSecondary => OrientationData {
                 orientation: Orientation::Landscape,
                 flipped: true,
-                natural: angle == 180,
+                natural: if angle == 180 { Orientation::Landscape } else { Orientation::Portrait },
             },
             OrientationType::PortraitPrimary => OrientationData {
                 orientation: Orientation::Portrait,
                 flipped: false,
-                natural: angle == 0,
+                natural: if angle == 0 { Orientation::Portrait } else { Orientation::Landscape },
             },
             OrientationType::PortraitSecondary => OrientationData {
                 orientation: Orientation::Portrait,
                 flipped: true,
-                natural: angle == 180,
+                natural: if angle == 180 { Orientation::Portrait } else { Orientation::Landscape },
             },
             _ => {
                 unreachable!("found unrecognized orientation: {}", orientation.type_string())

src/platform_impl/web/window.rs

@@ -312,7 +312,7 @@ impl Inner {
     #[inline]
     pub(crate) fn fullscreen(&self) -> Option<Fullscreen> {
         if self.canvas.is_fullscreen() {
-            Some(Fullscreen::Borderless(None))
+            Some(Fullscreen::Borderless(Some(self.monitor.current_monitor())))
         } else {
             None
         }