Make all script validation flags backward compatible #10699

This change makes SCRIPT_VERIFY_UPGRADABLE_NOPS not apply to OP_CHECKLOCKTIMEVERIFY and OP_CHECKSEQUENCEVERIFY. This is a no-op as UPGRADABLE_NOPS is only set for mempool transactions, and those always have SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY and SCRIPT_VERIFY_CHECKSEQUENCEVERIFY set as well. The advantage is that setting more flags now always results in a reduction in acceptable scripts (=softfork).

This results in a nice and testable property for validation, for which a new test is added.

This also means that the introduction of a new definition for a NOP or witness version will likely need the following procedure (example OP_NOP8 here)

• Remove OP_NOP8 from being affected by SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS.
• Add a SCRIPT_VERIFY_DISCOURAGE_NOP8, which only applies to OP_NOP8.
• Add a SCRIPT_VERIFY_NOP8 which implements the new consensus logic.
• Before activation, add SCRIPT_VERIFY_DISCOURAGE_NOP8 to the mempool flags.
• After activation, add SCRIPT_VERIFY_NOP8 to both the mempool and consensus flags.

Can you rebase this on top of the now-merged #10192 to remove the extra checks in its test? Concept ACK.

Done.

utACK 01013f5d2fbe3fa86565c927bf7bb8ec0f525073 I did check some of the test changes failed appropriately, but wouldnt really call it a tested ACK per se.

utACK 01013f5

utACK 2851b77312b55c8868acd4cd2c118e5a034606b7, reviewed both test and interpreter changes, they seem clear and contained and could discover no issues with the changed logic.