Implement contract call script decoding

[danielbate]

Consumers of the SDK may want to extract the scriptData from a transaction to see function / arguments / asset / forward amount / gas values by decoding the contract call script. An advanced user that knows our call script and the encoding used could reverse engineer this themselves. However we should provide a utility to assist with this to make this information more easily available. It could be used in the transaction summary, as expressed in #2530.

Reference:

• Is the "param1" of the call receipt no longer the function selector on the testnet? #2424