Restoration of disabled script (Tapleaf 0xC2).

Would add a new Taproot script version that brings back script commands switched off in Bitcoin's early days, with larger limits.

Many script commands were disabled early on because they could make nodes do too much work. This BIP would re-enable them in a new kind of Taproot script, raise size limits and allow much bigger numbers, relying on the cost budget in BIP 440 to stop scripts that are too slow to check.