Make egui work on WebGPU out of the box. (#2945)

* Make wgpu webgl/gles opt-in (but still work out of the box via feature flag), workaround canvas creation issue

* missing allow unsafe code annotations

* add breaking change not to eframe release notes

* Add --webgpu flag to build_demo_web.sh

* Improve CHANGELOG docs

* Clean up, and prepare for having to wasm:s

* put canvas without workaround under `if false`

* fix spelling

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Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/eframe/src/epi/mod.rs

@@ -498,8 +498,8 @@ impl Default for WebOptions {
 
             #[cfg(feature = "wgpu")]
             wgpu_options: egui_wgpu::WgpuConfiguration {
-                // WebGPU is not stable enough yet, use WebGL emulation
-                backends: wgpu::Backends::GL,
+                // Use WebGPU or WebGL. Note that WebGL needs to be opted in via a wgpu feature.
+                backends: wgpu::Backends::BROWSER_WEBGPU | wgpu::Backends::GL,
                 device_descriptor: wgpu::DeviceDescriptor {
                     label: Some("egui wgpu device"),
                     features: wgpu::Features::default(),