wallet: include input values during utxo selection and tx validation
wallet: include input values during utxo selection and tx validation

When spending a segwit output, the wallet also needs the input value of
the previous output script. Therefore when selecting outputs the input
value is now returned. Additionally when validating newly signed
outputs the input value as also passed into `txscript.Engine`

btcsuite/btcwallet,btcsuite/btcwallet