Add support for using Dawn as the WebGPU backend

[rdw-software]

If the API is identical now it should "just work", but it'd still be useful to have tests for this (CI workflows).

While trying to build Dawn manually, there have been numerous issues though:

• Building shared libraries caused linker errors due to multiple symbols even on MSVC
• Building on MSYS2 via MINGW didn't work at all (crashes my PC every time if using VK only)
• No idea how to use DirectX with MINGW, it failed to compile some of the Windows SDK headers
• Building in WSL caused compiler errors (need to test on a real Linux system)
• There were compiler warnings that failed the build process (due to -Werror being set)
• Building on OSX with the Metal backend has yet to be tested