[64-bit ints] Add activation logic

Summary:
After this diff, 63+sign-bit integers will be enabled with the Shibusawa upgrade.

Before activation, Scripts of the kind 0x11_0000_0000 0x10_0000_0000 OP_ADD 0x21_0000_0000 OP_EQUAL are unspendable, as they exceed the 31+sign-bit range that is currently active on Script.

After activation, they will become valid, as well as with all other arithmetic opcodes.

Activation code inspired by D13159.

Depends on D18462 and D18481.

Test Plan: ninja check-functional

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D18469