* Validate transparent coinbase output maturity and shielding
- Add a CoinbaseSpendRestriction enum and Transaction method
- Validate transparent coinbase spends in non-finalized chains
* Don't use genesis created UTXOs for spends in generated block chains
* Refactor out a new_transaction_ordered_outputs function
* Add Transaction::outputs_mut for tests
* Generate valid transparent spends in arbitrary block chains
* When generating blocks, fixup the block contents, then the block hash
* Test that generated chains contain at least one transparent spend
* Make generated chains long enough for reliable tests
* Add transparent and shielded input and output methods to Transaction
* Split chain generation into 3 functions
* Test that unshielded and immature transparent coinbase spends fail
* Comment punctuation
* Clarify a comment
* Clarify probability calculation
* Test that shielded mature coinbase output spends succeed
* Add an OrderedUtxo type for validation of spends within a block
This change allows us to check that transparent spends use outputs from
earlier in their block. (But we don't actually do that check yet.)
We need to keep the order of UTXOs when we're contextually verifying
each new block that is added to a chain. But the block order is
irrelevant for UTXOs stored in the state.
* Take ownership in utxos_from_ordered_utxos
* Delete a confusing comment