Remove coinselection.h -> wallet.h circular dependency

Summary:
Changes CInputCoin to coinselection and to use CTransactionRef in
order to avoid a circular dependency. Also moves other coin selection
specific variables out of wallet.h to coinselectoin.h

This is a partial backport of Core PR10637 : https://github.com/bitcoin/bitcoin/pull/10637/commits/4b2716da46e96c45206db869b83c28c5fc7889f4

Depends on D3245 and D3249

Test Plan:

make check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3250