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>
c9b24d5a5c