test: add unit test for non-standard bare multisig txs

Summary:

The function IsStandardTx() returns rejection reason "bare-multisig" if the
transaction has a bare multisig output and the policy flag fIsBareMultisigStd
is false (set by the boolean command-line argument "-permitbaremultisig" -- for
the unit test, we simply set the global flag variable directly).

This is a backport of Core PR17502

Test Plan: ninja && ninja check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D8308