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-wgpu/src/renderer.rs

@@ -293,6 +293,7 @@ impl Renderer {
                         // 2: uint color
                         attributes: &wgpu::vertex_attr_array![0 => Float32x2, 1 => Float32x2, 2 => Uint32],
                     }],
+                    compilation_options: wgpu::PipelineCompilationOptions::default()
                 },
                 primitive: wgpu::PrimitiveState {
                     topology: wgpu::PrimitiveTopology::TriangleList,
@@ -334,6 +335,7 @@ impl Renderer {
                         }),
                         write_mask: wgpu::ColorWrites::ALL,
                     })],
+                    compilation_options: wgpu::PipelineCompilationOptions::default()
                 }),
                 multiview: None,
             }