Refactor w3up-client to pass Space via agent.delegate method

[fforbeck]

Allow a space that isn't the current space to be passed to agent.delegate method.

This would allow us to get rid of the currentSpace concept more easily because right now the delegate assumes we are operating with the currentSpace so we often need to set it before calling the delegation method.

More info: storacha/w3up#1551 (comment)

Once that is implemented, we can refactor the client.shareSpace (code) method to remove the Space reset logic because we will provide the space DID as part of the delegate call.

[fforbeck]

cc: @alanshaw