Enable WebGPU backend in wgpu by default instead of WebGL

Instead, we expose a new `webgl` feature.

wgpu/Cargo.toml

@@ -12,6 +12,7 @@ geometry = ["iced_graphics/geometry", "lyon"]
 image = ["iced_graphics/image"]
 svg = ["resvg"]
 web-colors = ["iced_graphics/web-colors"]
+webgl = ["wgpu/webgl"]
 
 [dependencies]
 wgpu = "0.17"
@@ -24,9 +25,6 @@ once_cell = "1.0"
 rustc-hash = "1.1"
 log = "0.4"
 
-[target.'cfg(target_arch = "wasm32")'.dependencies]
-wgpu = { version = "0.17", features = ["webgl"] }
-
 [dependencies.twox-hash]
 version = "1.6"
 default-features = false