Add pubkeys and whether input was witness to SignatureData

Summary:
Stores pubkeys in SignatureData and retrieves them when using GetPubKey().

Stores whether the signatures in a SignatureData are for a witness input.

This is a partial backport of Core PR13557 : https://github.com/bitcoin/bitcoin/pull/13557/commits/12bcc64f277f642ece03c25653e726f2276f0d51

Depends on D4258

Test Plan: Unfortunately, The PR dump all the tests at once at the end, so there are n test for the new code.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D4285