[Cashtab] [chronik utxo handling p2] Add a function to split utxos by slp, nonSlp to match current storage model

Summary:
T2447

Depends on D11928

Add a function to split slp and nonSlp utxos.

With chronik, any token that has an slpToken key is an slp utxo. Function with unit test added.

Test Plan:
npm start
Confirm slpUtxos.length + nonSlpUtxos.length in chronikSlpBalancesAndUtxos === chronikUtxos.length
Review new unit test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D11933