Update to wgpu 0.20 (#4433)

updates the wgpu version to 0.20 and changes the API calls accordingly. 
I had to update wasm-bindgen to "0.2.92". Otherwise, I got this error
for the demo app:
```
error: failed to select a version for `wasm-bindgen`.
    ... required by package `js-sys v0.3.69`
    ... which satisfies dependency `js-sys = "^0.3.69"` of package `eframe v0.27.2 (/home/user/Projects/egui/crates/eframe)`
    ... which satisfies path dependency `eframe` (locked to 0.27.2) of package `confirm_exit v0.1.0 (/home/user/Projects/egui/examples/confirm_exit)`
versions that meet the requirements `^0.2.92` are: 0.2.92

all possible versions conflict with previously selected packages.

  previously selected package `wasm-bindgen v0.2.90`
    ... which satisfies dependency `wasm-bindgen = "=0.2.90"` of package `egui_demo_app v0.27.2 (/home/user/Projects/egui/crates/egui_demo_app)`

failed to select a version for `wasm-bindgen` which could resolve this conflict
```

Why is it locked to this version right now?

I ran the tests, checked the web demo and my own projects, and
everything seems to work fine with wgpu 0.20.

---------

Co-authored-by: Andreas Reich <r_andreas2@web.de>

crates/egui_demo_app/src/apps/custom3d_wgpu.rs

@@ -49,11 +49,13 @@ impl Custom3d {
                 module: &shader,
                 entry_point: "vs_main",
                 buffers: &[],
+                compilation_options: wgpu::PipelineCompilationOptions::default(),
             },
             fragment: Some(wgpu::FragmentState {
                 module: &shader,
                 entry_point: "fs_main",
                 targets: &[Some(wgpu_render_state.target_format.into())],
+                compilation_options: wgpu::PipelineCompilationOptions::default(),
             }),
             primitive: wgpu::PrimitiveState::default(),
             depth_stencil: None,