Enable disconnecting two selected ways from each other

[quincylvania]

Since we did #4245 you've been able to disconnect the selected way from all connected ways. You can select specific vertices to limit the disconnection. We should also allow limiting by connected ways, i.e. only shared nodes are disconnected.

Example use case:

[quincylvania]

I did this! It feels like a natural interaction, I'm sure mappers expected it to work like this already. As a bonus, you can also run Disconnect on multiple ways that don't share nodes, disconnecting them each entirely.