https://github.com/bitcoin/bitcoin/pull/16944/commits/39465d545d521e66bb3accfa788aa94bffaf47eb
Note to reviewers: Original PR has a default SigHashType argument for fillPSBT set in both the declaration and definition, I've removed the default from the definition as it's DRYer and less error-prone that way
Partial backport of Core PR16944
Depends on D7294