IsStandard should check the witnessprogram is a valid point on the field #24631

Is your feature request related to a problem? Please describe. A v1 taproot witness program must be a valid point on secp256k1 otherwise it is essentially a black hole.

Describe the solution you'd like Add a check in IsStandard that will check the witnessprogram in the case where WITNESS_V1 is returned. If the witness program is not the X value of a valid point, return false. (https://github.com/bitcoin/bitcoin/blob/v22.0/src/policy/policy.cpp#L53-L74)

There has been a pull request with that policy change already (#24106), but it was rejected with quite convincing reasons, e.g. potential problems in batching transactions for exchanges. See in particular the answers #24106 (comment), #24106 (comment) and #24106 (comment).