refactor: Move SendCoinsRecipient in own header

Summary:
Co-authored-by: Gregory Sanders <gsanders87@gmail.com>

Backport of Core PR17513 - Part 1 of 4.

Test Plan: ninja && ninja check

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7572