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