[cashtab] Always show 2 decimals for amounts < 1k XEC

Summary:
A tx that sends 42 XEC will show 42 XEC, then 42.00 XEC if clicked (because it now shows the detailed amount). While this feature is useful for amounts > 1000 because there is a change in units (k, M, B, etc.) this is confusing for plain XEC. This is looking even worse if the amount is a single decimal like 42.1 XEC.

Always use 2 decimals for amounts below 1k XEC.

Depends on D17450

Test Plan:

npm run test
npm run start

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D17451