[alias-server] [p6] outputScriptToAddress function and unit tests

Summary:
T2922

Depends on D13078

Add a function to get P2SH or P2PKH ecash: address from an outputScript. Add unit tests.

The next diff in this stack will implement this function in getAliases and add unit tests there.

Test Plan:
Review function and unit tests
npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D13079