Make PUSHDATA opcodes have names in ParseScript

Summary:
Currently, ParseScript does not recognize scripts which use the
full PUSHDATA opcode names. This commit enables the parser to
recognize these opcodes, and fixes script_tests.json to have
PUSHDATA opcodes be explicitly named.

Test Plan:

make check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1306