Add support for forkid in GetScriptAsm
Summary: This ensure that GetScriptAsm is able to represent apropriately hashtype using SIGHASH_FORKID.
Test Plan: Added unit tests for the new cases.
Reviewers: freetrader, sickpig, awemany, kyuupichan, #bitcoin_abc
Reviewed By: freetrader, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D308