mr_gpu_triangle_example

Using wio for windowing, and zig for shader lang

Uses a switch in the vertex shader instead of the regular const array because of ziglang/zig#31925, but a fix is in the master branch of zig. But zig->spirv needs int8 and in16, maybe because of that switch? Which aren't enabled in mr_gpu atm and I don't see a way to pass features to enable in. I just edited my zig-pkg's copy of mr_gpu's feature setting up to add int8 and int16 as silly workaround for now.