Create wallet RPCs for PSBT

Summary:
walletprocesspsbt takes a PSBT format transaction, updates the
PSBT with any inputs related to this wallet, signs, and finalizes
the transaction. There is also an option to not sign and just
update.

walletcreatefundedpsbt creates a PSBT from user provided data
in the same form as createrawtransaction. It also funds the transaction
and takes an options argument in the same form as fundrawtransaction.
The resulting PSBT is blank with no input or output data filled
in.

This is a partial backport of Core PR13557 : https://github.com/bitcoin/bitcoin/pull/13557/commits/a4b06fb42eb0ad94e562ca839391b57e69285136

Depends on D4351

Test Plan: Unfortunately, the test have all been dumped at once at the end.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4352