Moving VMs from VirtualBox to Client Hyper-V

I've decided to move the VMs on my desktop from VirtualBox to Microsoft Hyper-V. Because reasons.

Actually because I've upgraded my desktop to an AMD Ryzen CPU: first, AMD-V/SVM is not supported by the Intel HAXM thing from the Android SDK, so I wanted to try out Microsoft's Hyper-V based Android "emulator" (VM configurator/runner thingy) instead. Second, giving 16 virtual CPUs on an SMT 8-core to a FreeBSD guest in VirtualBox results in a weird performance issue. (Though giving 4 vCPUs to multiple VMs on a 4-core CPU worked fine.) Third, it's Oracle VM VirtualBox and …