Builtin implementations of sdl2.dll + webgpu.dll

[mateli]

Create a sdl2 wrapper with WebGPU support and port sample applications that already works with emscripten. This would cover wasi-webgpu when using retrowin32 for web development.

Create both native and emulated dll's so that applications can be developed and run both in retrowin32 and 32 bit windows. Perhaps also wine?