Feature proposal: batch instruction

[joncinque]

Problem

p-token has added a "batch" instruction, which is useful to avoid overhead when CPI'ing. Token-2022 doesn't have a batch instruction.

Proposed solution

Add a similar batch instruction to token-2022! We'll just need to be very careful to avoid falling into any spoofing traps, and explicitly do all account ownership checks in the batch instruction, similar to how p-token does it.