Can't set MSAA samples beyond 4

[swiftcoder]

Description
A clear and concise description of what the bug is.

The Vulkan capabilities viewer says that my hardware/driver supports MSAA samples up to 8 for all targets:

Setting MSAA samples to 1 or 4 works correctly, however increasing the samples to 8 causes the following error:

     Running `C:\...\msaa-line.exe`
Using NVIDIA GeForce GTX 1080 (Vulkan)
[2022-07-23T09:22:55Z ERROR wgpu::backend::direct] Handling wgpu errors as fatal by default
thread 'main' panicked at 'wgpu error: Validation Error

Caused by:
    In a RenderPass
      note: encoder = `<CommandBuffer-(0, 1, Vulkan)>`
    In a pass parameter
      note: command buffer = `<CommandBuffer-(0, 1, Vulkan)>`
    attachment's sample count 8 is invalid

', wgpu\src\backend\direct.rs:2391:5

Repro steps
Modify the msaa-line sample to set the number of samples to 8, and run it.

Expected vs observed behavior
Clearly describe what you get, and how it goes across your expectations.

I appreciate that the current web spec only supports sample counts of 1 or 4, but I don't think this limitation should be enforced as a strict validation (especially for desktop builds, where the driver likely supports at least 8, and one can always query against the underlying API directly).

Extra materials
This appears to be failing a hardcoded validation.

All other hardcoded validations I can find only check that the number of samples are less than 32.

Platform
Information about your OS, version of wgpu, your tech stack, etc.

Windows 10, Vulkan, v0.13.1 of wgpu

[cwfitzgerald]

Thanks for the issue! We definitely want to add this, and the way I think that this should manifest is by extending the TextureFormatFeatutes and splitting multisampling into three flags, 2, 4, and 8 sample flags for each texture.