Wgpu

Changed:

* Update to the latest wgpu-native (including latest Naga).
* The power-preference is actually taken into account.
* The adapter actually reports its limits.
* The limits in `request_device` are actually used.
* The `Adapter.is_software` property is renamed to `Adapter.is_fallback_adapter`.

Added:

* An offscreen canvas to take snapshots without needing a window.

Changed:

* On Windows, the Vulkan backend is now forced unless `WGPU_BACKEND_TYPE` is set.

Fixed:

* Better support for multiple canvases by fixing a specific Qt issue.
* Fixed that canvas was not passed to low level function of `request_adapter`.
* Support calling `get_current_texture()` multiple times during a draw.

Added:

* The wgpu backend can be forced using the `WGPU_BACKEND_TYPE` env variable.
Values can be e.g. "D3D12", "Metal", "Vulkan".
* Initial support for off-screen canvases.
* Adds `adapter.is_software` property.

Changed:

* The `GPUPresentationContext` class has been renamed to `GPUCanvasContext`.
* The functionality of the swap-chain has moved to the `GPUCanvasContext`.
* The now removed `GPUSwapChain` was used as a context manager. Instead,
the frame is presented (ala GL swapbuffers) automatically at the end of a draw.
* The `canvas.configure_swap_chain()` method has been removed. Instead,
`canvas.get_context()` should be used, to obtain a present/canvas context.
* The `adapter.request_device()` method has its arguments `non_guaranteed_features`
and `non_guaranteed_limits` replaced with `required_features` and `required_limits`.
* The enum field `StoreOp.clear` is now `StoreOp.discard`.
* The flag field `TextureUsage.SAMPLED ` is now `TextureUsage.TEXTURE_BINDING `.
* The flag field `TextureUsage.STORAGE ` is now `TextureUsage.STORAGE_BINDING `.
* The enum `InputStepMode` is now `VertexStepMode`.
* WGSL: `arrays` must be declared as `var` (not `let`) in order to allow dynamic indexing.
* WGSL: storage classes are written differently.

Changed:

* The backend selection is automatic by default. To force a backend, the `WGPU_BACKEND_TYPE` environment variable can be set to e.g. "Vulkan". It could be good to do this on Windows to prevent selection of DX12 for now.

Added:

* `adapter.properties` now has actual values, allowing inspection of the selected
GPU and backend.
* Added back support for filtering float32 textures by enabling a certain wgpu feature
by default.

Fixed:

* An error in the docs of `create_render_pipeline`.
* Vulkan backend is now forced to prevent DX12 being select and causing probems
because it's less mature.

This release uses a new version of wgpu-native which has changed quite a bit internally. There
is more validation (thus more restrictions). There are only a few changes to the API.
However, one big change is that shaders can now be provided as both SpirV and WGSL. Due to
the strict validation, most shaders compiled by PyShader are not usable anymore. We
recommend using WGSL instead.

Added:

* Added `GPUAdapter.properties` (the amount of information it contains will increase in the future).
* Added proper support for WGSL.

Changed:

* Renamed `renderpass.set_blend_color` -> `set_blend_constant`.
* Stricter validation of SpirV shaders.
* Float32 texture formats must now use a non-filtering sampler and texture-sample-type.
* Integer texture formats can no longer use a texture (use `textureLoad` instead).
* ... and more tighter restrictions.

Removed:

* The API concerning debug markers and groups is temporarily removed.
* Adapter and device features is temporarily removed.
* Adapter and device limits is temporarily removed.