SG_VERTEXFORMAT_HALF3 is not defined in sg_vertex_format

[rcases]

SG_VERTEXFORMAT_HALF3 is not defined in sg_vertex_format but is used in webgpu backend in _sg_wgpu_vertexformat function
you probably meant SG_VERTEXFORMAT_HALF4, but it would be nice if SG_VERTEXFORMAT_HALF3 existed

[floooh]

Yeah it's a typo. HALF3 support is unlikely though because at least WebGPU only supports float16x2 and float16x4:

https://www.w3.org/TR/webgpu/#enumdef-gpuvertexformat

Btw, don't use the WebGPU backend in master, it's incomplete and broken. I'm currently working on 'final' WebGPU support in the sgfx-wgpu branch (you can follow this PR to get an idea how close to merge this is: #865)