Catch up to latest VHDX v2(=0x01) rev-7.0 specification
Additional information:
Below issues need to be addressed before or during the tackling of this issue.
- ~#727 VHDX is corrupted on expansion.~
- #136 windows qemu-img create vpc/vhdx error due to sparse files
- #1605 On windows, 2nd kind vhdx-dyn bug, crash on Unexpected error in bdrv_check_qiov_request() in io.c 
- #806 Fixed VHDX inflates beyond its fixed size when data is copied onto it and also corrupts
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This VHDX support applies to qemu build on any architecture, not just the windows-build.

It is very likely, that the native hypervisor on windows WHPX will be the main hypervisor displacing haxm/vbox etc. VHDX, if it works, seems to be the virtual-disk format that is ideal 
- for Linux/windows dual-boot machines, 
- for clusters with Linux/windows servers sharing images from a network-storage  
- for WSL2/Hyper-V

Following a similar line of thought, NTFS/ExFat may be ideal for sharing data/images between Linux and Windows. So the storing, modification and drive attachment of VHDX files on these filesystems need to be just as well-tested as native Linux filesystems. As their driver are internal-kernel-drivers and not fuse/dokan-drivers, on both operating-systems, they are also performant.