Build 20175

For general Windows information on build 20175 visit the Windows blog.

• Adjust default memory assignment of WSL2 VM to be 50% of host memory or 8GB, whichever is less [GH 4166].
• Change \\wsl$ prefix to \\wsl to support URI parsing. The old \\wsl$ path is still supported.
• Enable nested virtualization for WSL2 by default on amd64. You can disable this via %userprofile%\.wslconfig ([wsl2] nestedVirtualization=false).
• Make wsl.exe --update demand start Microsoft Update.
• Support renaming over a read-only file in DrvFs.
• Ensure error messages are always printed in the correct codepage.