Merge bitcoin/bitcoin#32521: policy: make pathological transactions packed with legacy sigops non-standard

96da68a38f qa: functional test a transaction running into the legacy sigop limit (Antoine Poinsot)
367147954d qa: unit test standardness of inputs packed with legacy sigops (Antoine Poinsot)
5863315e33 policy: make pathological transactions packed with legacy sigops non-standard. (Antoine Poinsot)

Pull request description:

  The Consensus Cleanup soft fork proposal includes a limit on the number of legacy signature
  operations potentially executed when validating a transaction. If this change is to be implemented
  here and activated by Bitcoin users in the future, we should make transactions that are not valid
  according to the new rules non-standard first because it would otherwise be a trivial DoS to
  potentially unupgraded miners after the soft fork activates.

  ML post: https://gnusha.org/pi/bitcoindev/49dyqqkf5NqGlGdinp6SELIoxzE_ONh3UIj6-EB8S804Id5yROq-b1uGK8DUru66eIlWuhb5R3nhRRutwuYjemiuOOBS2FQ4KWDnEh0wLuA=@protonmail.com/T/#u

ACKs for top commit:
  instagibbs:
    reACK 96da68a38f
  maflcko:
    review ACK 96da68a38f 🚋
  achow101:
    ACK 96da68a38f
  glozow:
    light code review ACK 96da68a38f, looks correct to me

Tree-SHA512: 106ffe62e48952affa31c5894a404a17a3b4ea8971815828166fba89069f757366129f7807205e8c6558beb75c6f67d8f9a41000be2f8cf95be3b1a02d87bfe9

test/functional/test_framework/script_util.py

@@ -35,6 +35,12 @@ from test_framework.script import (
     hash160,
 )
 
+# Maximum number of potentially executed legacy signature operations in validating a transaction.
+MAX_STD_LEGACY_SIGOPS = 2_500
+
+# Maximum number of sigops per standard P2SH redeemScript.
+MAX_STD_P2SH_SIGOPS = 15
+
 # To prevent a "tx-size-small" policy rule error, a transaction has to have a
 # non-witness size of at least 65 bytes (MIN_STANDARD_TX_NONWITNESS_SIZE in
 # src/policy/policy.h). Considering a Tx with the smallest possible single