Added functional tests for PSBT that test the RPCs. Also added all
of the BIP 174 test vectors (except for the updater tests) in the
Added a Unit test for the BIP 174 updater test vector.
This is a partial backport of Core PR13557 : https://github.com/bitcoin/bitcoin/pull/13557/commits/020628e3a4e88e36647eaf92bac4b3552796ac6a
Depends on D4352