Make size/position types generic over pixel type (#1277)

* Begin implementing DPI generics

* Fix multithreaded example

* Format

* Fix serde test

* hopefully fix most of the errors

* Fix dpi module errors

* More error fixings

* Format

* fix macos errors

* Another error pass

* Replace bad type signatures

* more fixins

src/platform_impl/web/stdweb/canvas.rs

@@ -96,7 +96,7 @@ impl Canvas {
         self.raw.height() as f64
     }
 
-    pub fn set_size(&self, size: LogicalSize) {
+    pub fn set_size(&self, size: LogicalSize<f64>) {
         self.raw.set_width(size.width as u32);
         self.raw.set_height(size.height as u32);
     }