A set of useful proc macros for wgpu.
Generates a wgpu::VertexBufferLayout,
accessible through a LAYOUT constant on the struct.
There is an additional layout helper attribute macro that can be specified on
the struct, which allows specifying the step_mode.
Possible values are Vertex & Instance, and by default, the value is Vertex.
The layout helper attribute macro also can be used on individual fields to
either override the generated VertexFormat by specifying a
VertexFormat variant, or to specify if the norm version of
the generated VertexFormat should be used (so Uint8 becomes Unorm8).