Enhance address change functionality

[NoahAndrews]

Changing the Expansion Hub address should optionally (defaulting to true) perform discovery to check that no other devices on the bus have the same address. Additionally, ParentExpansionHub should have a discoverChildren(openNewlyFoundChildren: boolean = true) method that allows the application to prevent the user from selecting an address that's already being used on the bus.

[LandryNorris]

Right now, we always open RevHub objects when we create them, meaning the user never has to worry about whether a hub has been opened. We could instead create a getChildAddresses(): number[] that lists child addresses instead of creating RevHub objects that aren't opened, and a discoverChildren(): RevHub[] that unconditionally opens the children. This keeps the current behavior where we only return opened RevHubs.

[NoahAndrews]

I agree with the approach, but I don't love the names. Maybe "findAddressesOfPotentialChildren" and "openAllChildren"? The first one is tricky, since we don't want to give the impression that we're just listing the addresses of the children that we're currently communicating with. The doc comment will need to spell out what's happening clearly.

[LandryNorris]

findAddressesOfRs485ConnectedChildren? It's quite long, but indicates what the devices are. Maybe devices is a better name than children in this case?

[NoahAndrews]

findAddressesOfUsbConnectedChildren? It's quite long, but indicates what the devices are. Maybe devices is a better name than children in this case?

It's RS-485 not USB, but otherwise I like it.

The other thing to consider is the Control Hub, where we'll need to support doing this for USB and RS-485 children.

[LandryNorris]

How about findAddressesOfAllChildDevicesConnectedToThisExpansionOrControlHubWhichMayBeConnectedViaRs485OrUsb()?