[alias-server] Use ecash-script to parse alias registrations according to latest spec

Summary:
T3060

Responding to feedback of D13916. With ecash-script library developed and the spec finalized, implement here.

Key change is modifying the parseAliasTx function. This change requires new mocks, which requires changes to most unit test files.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14067