Fix documentation for file drag and drop (emilk#5328)

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The `RawInput::dropped_files` documentation referred to `NativeOptions`,
but the `drag_and_drop` option was moved to `ViewportBuilder` and is now
enabled by default.

Note that drag-and-drop is not *explicitly* enabled by default here, but
rather is enabled by default in winit. We only override winit's default
if the API consumer specifies it. It might be a good idea in general to
provide explicit defaults for everything in `ViewportBuilder` so we're
not relying on winit's behavior, but that's best left for another PR.

* Closes N/A
* [x] I have followed the instructions in the PR template

crates/egui/src/data/input.rs

@@ -68,8 +68,8 @@ pub struct RawInput {
 
     /// Dragged files dropped into egui.
     ///
-    /// Note: when using `eframe` on Windows you need to enable
-    /// drag-and-drop support using `eframe::NativeOptions`.
+    /// Note: when using `eframe` on Windows, this will always be empty if drag-and-drop support has
+    /// been disabled in [`crate::viewport::ViewportBuilder`].
     pub dropped_files: Vec<DroppedFile>,
 
     /// The native window has the keyboard focus (i.e. is receiving key presses).

crates/egui/src/viewport.rs

@@ -534,7 +534,7 @@ impl ViewportBuilder {
     /// See [winit's documentation][drag_and_drop] for information on why you
     /// might want to disable this on windows.
     ///
-    /// [drag_and_drop]: https://docs.rs/winit/latest/x86_64-pc-windows-msvc/winit/platform/windows/trait.WindowBuilderExtWindows.html#tymethod.with_drag_and_drop
+    /// [drag_and_drop]: https://docs.rs/winit/latest/x86_64-pc-windows-msvc/winit/platform/windows/trait.WindowAttributesExtWindows.html#tymethod.with_drag_and_drop
     #[inline]
     pub fn with_drag_and_drop(mut self, value: bool) -> Self {
         self.drag_and_drop = Some(value);