script_tests signature function renames to add "ECDSA"

Summary:
Now that Schnorr sigs are there, would be nice to disambiguate both ways. Changes:
DoSign -> DoSignECDSA
PushSig -> PushSigECDSA
PushDataSig -> PushDataSigECDSA

(I left sign_multisig untouched even though it's ECDSA-only; there is no Schnorr counterpart.)

Test Plan: make check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Maniphest Tasks: T527

Differential Revision: https://reviews.bitcoinabc.org/D2515