[enhancement] Enable logic similar to TS SDK .gas psuedo coin

[FrankC01]

This will enable things like starting a transaction with only 1 coin to start with.

Fundementally, it also enables things like coin = txn.split_coin(txn.gas,amounts=[1000000])

[FrankC01]

This works.

    client = SuiClient(SuiConfig.default_config())
    txer = SuiTransaction(client)
    spcoin = txer.split_coin(coin=bcs.Argument("GasCoin"), amounts=[1000000])
    txer.transfer_objects(transfers=[spcoin], recipient=client.config.active_address)