344: Use the new map-async r=kvark a=kvark
Depends on https://github.com/gfx-rs/wgpu/pull/675
It changes the API of mapping and removes `create_buffer_mapped`.
The new functionality is not implemented in Gecko yet, so this breaks the web target, for now.
Co-authored-by: Dzmitry Malyshau <kvarkus@gmail.com>