Web: handle None for depth_ops and stencil_ops

[niklaskorz]

Checklist

• Run cargo clippy.
• Run RUSTFLAGS=--cfg=web_sys_unstable_apis cargo clippy --target wasm32-unknown-unknown if applicable.
• Add change to CHANGELOG.md. See simple instructions inside file.

Connections
Link to the issues addressed by this PR, or dependent PRs in other repositories

There's no corresponding issue yet (should I create one?).

More or less depends on #3657 (at least to see the result), here's a branch merging both fixes for testing: https://github.com/niklaskorz/wgpu/tree/dynamic-dispatch-depth-fix

Description
Describe what problem this is solving, and how it's solved.

When using a DepthStencilState with a texture that only includes depth but not stencil data (e.g., TextureFormat::Depth32Float instead of TextureFormat::Depth24PlusStencil8), and then specifying stencil_ops: None in the RenderPassDepthStencilAttachment, Chrome Beta 113 reports the following:

stencilLoadOp is (LoadOp::Load) and stencilStoreOp is (StoreOp::Store) when stencilReadOnly (0) or the attachment ([TextureView of Texture "depth_texture"]) has no stencil aspect.
 - While validating depthStencilAttachment.
 - While encoding [CommandEncoder "encoder"].BeginRenderPass([RenderPassDescriptor "rpass"]).

This is fixed by not defining any stencil parameters on the web_sys::GpuRenderPassDepthStencilAttachment when stencil_ops is None.

Testing
Explain how this change is tested.

Tested on my project https://github.com/niklaskorz/linon using Chrome Beta 113 (see branch dynamic-dispatch-workaround, deployed on https://niklaskorz.github.io/linon/).

[teoxoy]

LGTM, thanks for the PR!