[Cashtab] Do not airdrop XEC to agora scripts

Summary:
The "holders" of the token qty offered in an Agora offer are the p2pkh addresses of the creating pk.

Make sure the airdrop function takes this into account. Otherwise we will airdrop XEC to Agora scripts.

We convert airdrop functions and tests to typescript to support this.

We also clean up the airdrop calculation functions. Behavior confirmed with existing tests.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D17357