[backport#15638] [build] Move rpc rawtransaction util functions to rpc/rawtransaction_util.cpp

Summary:
rpc/rawtransaction.cpp moves to libbitcoin_server since it should not be
accessed by non-node libraries. The utility following utility methods
move to their own unit rpc/rawtransaction_util since they need to be
accessed by non-node libraries:

• ConstructTransaction
• TxInErrorToJSON
• SignTransaction

https://github.com/bitcoin/bitcoin/pull/15638/commits/0509465542d63a5bbe7296f283f44dd491e74f78

Depends on D5979

This is a partial backport of Core PR15638

Test Plan:

ninja check check-functional

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5983