Tracking issue: Correct block version spec (MCIP 33)

[cbeck88]

During compatibility testing, we discovered that our assumptions in MCIP 26 are wrong:

• The status quo is not block version = 1, it is block version = 0. All blocks in prod right now are block version 0, and mc_transaction_core::BLOCK_VERSION is zero for clients in the wild now.
• The encrypted memos feature should be changed from block version 2 to block version 1.
• The confidential token ids feature should be changed from block version 3 to block version 2.

• Fix this in 1.2.0 release branch: decrement block version everywhere, bump to -pre2 #1698
• Fix this in master branch: decrement block version everywhere (master branch) #1700

MCIP 33 will correct the previous MCIPs. This is the tracking issue for this work.