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

[mkorbel1]

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