(Some) semantic transaction verification checks

[hdevalence]

Follow on to #1173, supersedes #1100. See those PRs for details.

[hdevalence]

There were some comments on these changes as part of that PR: #1100 (comment)

[teor2345]

It seems like we're missing the following semantic verification consensus rules:

Sorry for the mangled text, my PDF viewer doesn't seem to handle spaces in the Zcash Spec PDF.

•[Pre-Heartwood] Acoinbase transactionalsoMUST NOThave anyOutput descriptions.
•[Overwinteronward]nExpiryHeightMUSTbe less than or equal to 499999999.
•[Overwinteronward] If atransactionis not acoinbase transactionand itsnExpiryHeight�eld is nonzero,then itMUST NOTbe mined at ablock heightgreater than itsnExpiryHeight.
•[Saplingonward]valueBalanceMUSTbe in the range{−MAX_MONEY..MAX_MONEY}.
]
•[Heartwoodonward] AllSaplingoutputs incoinbase transactionsMUSTdecrypt to anote plaintext, i.e. theprocedure in§ 4.17.3‘Decryption using a Full Viewing Key (Sapling)’on p. 49 does not return⊥, using asequence of32zero bytes as theoutgoing viewing key.
•[Canopyonward] AnySaplingoutput of acoinbase transactiondecrypted to anote plaintextaccording tothe preceding ruleMUSThavenote plaintext lead byteequal to0x02. (This applies even during the “graceperiod” speci�ed in [ZIP-212].)

Are they on a tracking issue somewhere?

[dconnolly]

It seems like we're missing the following semantic verification consensus rules:

Sorry for the mangled text, my PDF viewer doesn't seem to handle spaces in the Zcash Spec PDF.

•[Pre-Heartwood] Acoinbase transactionalsoMUST NOThave anyOutput descriptions.
•[Overwinteronward]nExpiryHeightMUSTbe less than or equal to 499999999.
•[Overwinteronward] If atransactionis not acoinbase transactionand itsnExpiryHeight�eld is nonzero,then itMUST NOTbe mined at ablock heightgreater than itsnExpiryHeight.
•[Saplingonward]valueBalanceMUSTbe in the range{−MAX_MONEY..MAX_MONEY}.
]
•[Heartwoodonward] AllSaplingoutputs incoinbase transactionsMUSTdecrypt to anote plaintext, i.e. theprocedure in§ 4.17.3‘Decryption using a Full Viewing Key (Sapling)’on p. 49 does not return⊥, using asequence of32zero bytes as theoutgoing viewing key.
•[Canopyonward] AnySaplingoutput of acoinbase transactiondecrypted to anote plaintextaccording tothe preceding ruleMUSThavenote plaintext lead byteequal to0x02. (This applies even during the “graceperiod” speci�ed in [ZIP-212].)

Are they on a tracking issue somewhere?

This is an incomplete set of checks, I think we want to merge the ones we have and then keep adding more one at a time to see if they break anything.

[dconnolly]

valueBalance MUST be in the range{−MAX_MONEY..MAX_MONEY}.

I think this is handled by Amount

[dconnolly]

(This is currently expected to fail the build until some of the error casting/impls are worked out)