Support ContractPrincipals in addition to StandardPrincipals

Looks like #6107 is back! We were testing out some scenarios where we'd want to send fungible tokens from our extension wallet into a smart contract that our agent can vote from. When trying to transfer to a contract I get a quick error that I can't see, then when I try to complete the TX the To: field is blank. Should we be able to transfer to a contract principal the same as a standard account principal?