Add documentation on `Interface`s driving/receiving each other

### Motivation

The "pair_interface_test.dart" is currently the best place for documentation related to `driveOther`, `receiveOther`, `conditionalDriveOther`, and `conditionalReceiveOther`. It would be good to have them in the user guide as well.

### Desired solution

Add documentation in the user guide about interfaces to talk about ways to drive/receive (including conditionally) between interfaces so you don't have to refer to the test for the documentation.

### Alternatives considered

_No response_

### Additional details

_No response_