Build 20150

For general Windows information on build 20150 visit the Windows blog.

• WSL2 GPU compute see Windows blog for more information.
• Introduce wsl.exe --install command line option to easily set up WSL.
• Introduce wsl.exe --update command line option to manage updates to the WSL2 kernel.
• Set WSL2 as the default.
• Increase WSL2 vm graceful shutdown timeout.
• Fix virtio-9p race condition when mapping device memory.
• Don't run an elevated 9p server if UAC is disabled.