wayland: implement scaling

This involves many subsystems:

- config:
    - allow setting the connector scale
    - allow setting the cursor size
- cursors:
    - load server cursors for all requested sizes and scales
- wl_surface:
    - track the output the surface belongs to
    - send wl_surface.enter/leave
- wl_output:
    - implement wl_output.scale
- text:
    - pre-render texts for all used scales
- renderer:
    - properly align scale textures and rectangles
- wp_fractional_scale:
    - new interface for fractional scaling

src/ifs/wl_surface/wp_fractional_scale_v1.rs

@@ -0,0 +1,78 @@
+use {
+    crate::{
+        client::{Client, ClientError},
+        ifs::wl_surface::WlSurface,
+        leaks::Tracker,
+        object::Object,
+        utils::buffd::{MsgParser, MsgParserError},
+        wire::{wp_fractional_scale_v1::*, WpFractionalScaleV1Id},
+    },
+    std::rc::Rc,
+    thiserror::Error,
+};
+
+pub struct WpFractionalScaleV1 {
+    pub id: WpFractionalScaleV1Id,
+    pub client: Rc<Client>,
+    pub surface: Rc<WlSurface>,
+    pub tracker: Tracker<Self>,
+}
+
+impl WpFractionalScaleV1 {
+    pub fn new(id: WpFractionalScaleV1Id, surface: &Rc<WlSurface>) -> Self {
+        Self {
+            id,
+            client: surface.client.clone(),
+            surface: surface.clone(),
+            tracker: Default::default(),
+        }
+    }
+
+    pub fn install(self: &Rc<Self>) -> Result<(), WpFractionalScaleError> {
+        if self.surface.fractional_scale.get().is_some() {
+            return Err(WpFractionalScaleError::Exists);
+        }
+        self.surface.fractional_scale.set(Some(self.clone()));
+        Ok(())
+    }
+
+    pub fn send_preferred_scale(&self) {
+        self.client.event(PreferredScale {
+            self_id: self.id,
+            scale: self.surface.output.get().preferred_scale.get(),
+        });
+    }
+
+    fn destroy(&self, msg: MsgParser<'_, '_>) -> Result<(), WpFractionalScaleError> {
+        let _req: Destroy = self.client.parse(self, msg)?;
+        self.surface.fractional_scale.take();
+        self.client.remove_obj(self)?;
+        Ok(())
+    }
+}
+
+object_base! {
+    WpFractionalScaleV1;
+
+    DESTROY => destroy,
+}
+
+impl Object for WpFractionalScaleV1 {
+    fn num_requests(&self) -> u32 {
+        DESTROY + 1
+    }
+}
+
+simple_add_obj!(WpFractionalScaleV1);
+
+#[derive(Debug, Error)]
+pub enum WpFractionalScaleError {
+    #[error("Parsing failed")]
+    MsgParserError(#[source] Box<MsgParserError>),
+    #[error(transparent)]
+    ClientError(Box<ClientError>),
+    #[error("The surface already has a fractional scale extension attached")]
+    Exists,
+}
+efrom!(WpFractionalScaleError, MsgParserError);
+efrom!(WpFractionalScaleError, ClientError);