Move Debugger and Windowed to a better location

We move `renderer::Debugger` to `layout::Debugger` and
`renderer::Windowed` to `window::Renderer`.

native/src/window/renderer.rs

@@ -0,0 +1,58 @@
+use crate::MouseCursor;
+
+use raw_window_handle::HasRawWindowHandle;
+
+/// A renderer that can target windows.
+pub trait Renderer: crate::Renderer + Sized {
+    /// The settings of the renderer.
+    type Settings: Default;
+
+    /// The type of target.
+    type Target: Target<Renderer = Self>;
+
+    /// Creates a new window [`Renderer`].
+    ///
+    /// [`Renderer`]: trait.Renderer.html
+    fn new(settings: Self::Settings) -> Self;
+
+    /// Performs the drawing operations described in the output on the given
+    /// target.
+    ///
+    /// The overlay can be a bunch of debug text logs. It should be rendered on
+    /// top of the GUI on most scenarios.
+    fn draw<T: AsRef<str>>(
+        &mut self,
+        output: &Self::Output,
+        overlay: &[T],
+        target: &mut Self::Target,
+    ) -> MouseCursor;
+}
+
+/// A rendering target.
+pub trait Target {
+    /// The renderer of this target.
+    type Renderer;
+
+    /// Creates a new rendering [`Target`] from the given window handle, width,
+    /// height and dpi factor.
+    ///
+    /// [`Target`]: trait.Target.html
+    fn new<W: HasRawWindowHandle>(
+        window: &W,
+        width: u16,
+        height: u16,
+        dpi: f32,
+        renderer: &Self::Renderer,
+    ) -> Self;
+
+    /// Resizes the current [`Target`].
+    ///
+    /// [`Target`]: trait.Target.html
+    fn resize(
+        &mut self,
+        width: u16,
+        height: u16,
+        dpi: f32,
+        renderer: &Self::Renderer,
+    );
+}