Add DumpRegister

[tcNickolas]

Is your feature request related to a problem? Please describe.
When I work on larger code that might have several different qubit registers serving different purposes, I want to be able to dump just the state of some of them, not of all systems. Typically, in such scenarios I know that these qubits are not entangled with the rest of the system, for example:

• In the katas, ShowQuantumStateComparison reuses the input register to show multiple states that can be prepared from it, uncomputing the preparation operation between them. This is inconvenient, since the state preparation operation might not have an adjoint defined. Instead, we could allocate an extra register and print the state of just that register.
• Similarly, for oracle-based problems, I need to check if the state of the input register didn't change, and if it did, let the user know - ideally printing its state separately from the state of the target qubit that is also allocated at this time.

Describe the solution you'd like
DumpRegister functionality similar to that of DumpMachine but allowing to the state of just one register. (This was mentioned as part of #579, but I think it's worth a separate callout.)

If the qubits are entangled with others, I'm fine with a message telling me this, like the classic QDK did, I'm usually interested in cases when they're not.