
This Mesa code is for enabling GL-On-D3D12 for cases like Windows on ARM devices lacking native OpenGL drivers or cases like WSL-g for allowing graphics access to Windows Subsystem for Linux via D3D12. For where it was at OpenGL 4.3 at the start of the week on Mesa Git, OpenGL 4.6 is now possible along with the relevant SPIR-V pieces.
Jesse Natalie of Microsoft has become a prolific contributor to Mesa. With code merged yesterday he's implemented the remaining extensions for OpenGL 4.6 as well as flipped the switch on SPIR-V support. This merge is a great milestone for those having to resort on the latest OpenGL capabilities while being trapped within Microsoft's confines and lacking native OpenGL driver support.
OpenGL 4.6 debuted in 2017 with many new features for OpenGL while since then obviously much of the graphics API focus has transitioned to Vulkan.