Add typedef for buffer stride

[tangmi]

Adds the following:

/// An stride between elements inside a buffer, in bytes.
pub type Stride = u32;

Note that CommandBuffer::copy_query_pool_results's and Device::get_query_pool_results's stride parameters have changed from u64 to u32. I'm unsure of the implications of this, but I don't imagine nobody has a buffer with a stride > u32::max_value() (can backends even support buffers that large?). Please let me know if I should change this back!

PR checklist:

• [x] make succeeds (on *nix)
• [x] make reftests succeeds
• [x] tested examples with the following backends: Vulkan, DX11, DX12

[bors[bot]]

Build succeeded:

• Android Stable
• Dependency Check
• iOS Stable
• Web Assembly
• MacOS Stable
• MacOS Nightly
• Ubuntu Stable
• Ubuntu Nightly
• Windows Stable
• Windows Nightly