Implement Branch and Bound coin selection in a new file

Summary:
Create a new file for coin selection logic and implement the BnB algorithm in it.

This is a partial backport of Core PR10637 : https://github.com/bitcoin/bitcoin/pull/10637/commits/0185939be6f7c5554b864e33657ce610fd434e18

Unfortunately, the test has way more dependencies, so it'll have to come separately.

Depends on D3248

Test Plan:

make check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3249