Implement pure version of Canvas widget

Cargo.toml

@@ -41,7 +41,7 @@ smol = ["iced_futures/smol"]
 # Enables advanced color conversion via `palette`
 palette = ["iced_core/palette"]
 # Enables pure, virtual widgets in the `pure` module
-pure = ["iced_pure"]
+pure = ["iced_pure", "iced_graphics/pure"]
 
 [badges]
 maintenance = { status = "actively-developed" }