[avalanche] Reject blocks that don't have the staking rewards output

Summary:
This implements a new block policy to accept or reject the blocks depending on the presence of a correct staking reward output in the coinbase transaction.

Depends on D14438.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK, bytesofman

Reviewed By: #bitcoin_abc, PiRK, bytesofman

Subscribers: bytesofman, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14444