[ecash-coinselect] Update getInputUtxos to support N x p2pkh outputs

Summary:
T3225

As per feedback from D14417, this diff forms part of a series of diffs to incrementally implement the key concepts from D14417:

1. Get a working API for N x p2pkh outputs (this diff)
2. Extend with N x op_return
3. Extend with N x slp outputs
4. Extend with N x p2sh outputs

Unlike D14417 however, this API is more aligned with the existing coinselect module in passing an object array of outputs rather than using a singular output ammount.

Note: the scriptType gating logic between p2pkh and p2sh will be added when we get to the p2sh diff.

Test Plan: npm test

Reviewers: Fabien, bytesofman, #bitcoin_abc

Reviewed By: Fabien, bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D14475