Introduce strict-assertions feature flag

For now, this feature flag only enables validation
in `iced_wgpu`; which has become quite expensive
since its `0.20` release.

renderer/Cargo.toml

@@ -22,6 +22,7 @@ geometry = ["iced_graphics/geometry", "iced_tiny_skia?/geometry", "iced_wgpu?/ge
 web-colors = ["iced_wgpu?/web-colors"]
 webgl = ["iced_wgpu?/webgl"]
 fira-sans = ["iced_graphics/fira-sans"]
+strict-assertions = ["iced_wgpu?/strict-assertions"]
 
 [dependencies]
 iced_graphics.workspace = true