get Vulkan ICD compiling in WASM so layers can hook/preempt properly (Vulkan SDK for WASM territory)

[devshgraphicsprogramming]

We need DLLs working in WASM, you can do delay load on Linux actually if you want/need
https://github.com/yugr/Implib.so

The top DLL we need is the Vulkan Loader, it's basically like having a WASM SDK at this point
https://github.com/KhronosGroup/Vulkan-Loader
But obviously we won't be compiling a graphical configurator XD

Before getting Llvmpipe or Venus working we can compile the mock ICD just to test simple conformance tests and mocks to see driver choice functions correctly.
https://github.com/KhronosGroup/Vulkan-Tools/blob/main/icd/README.md

This mock ICD should be enough to test layer injection and loading, the basic (non syncval and GPU AV) validation layers don't actually need a functional vulkan device to work.

One Llvmpipe is in, we can test physical device reporting and choosing between two icds.