Configuring a single Ubuntu installation as a dual-boot option and a VirtualBox appliance under Windows 10

I often need to use Windows 10 and Ubuntu on the same machine within a single login session, so I run Ubuntu as a virtual machine in Oracle VirtualBox. But I also like to be able to boot my computer natively into Ubuntu, so a dual-boot configuration is optimal. To get the best of both worlds, I install Ubuntu in a dual-boot configuration alongside Windows, and configure VirtualBox to access the Ubuntu disk partitions as a raw disk image. This allows me to boot directly into Ubuntu, or boot the same Ubuntu installation from within Windows using VirtualBox.