Tails Cloner: unmount all filesystems on target device

This builds on !1359 (merged) for #20139 (closed).

Beyond fixing the issues on #20149 (closed) this branch also:

• makes it so that we don't list partitions (e.g. /dev/sda1) but instead devices (e.g. /dev/sda) which just makes more sense, and prevents some misunderstandings, like that you can install Tails to a particular partition without touching the rest of the device. The only exception is that we list partitions with Tails installed that are upgradeable, in which case we don't list/touch other partitions on the device (or the device itself).

• allows installing to a device with LUKS-encrypted partition, or that has no partition and is directly LUKS-encrypted (this was impossible before)

Closes #20149 (closed), #20252 (closed), #20195 (closed)