VSize fails to account for sigops/datacarriercost in many instances

[luke-jr]

In various locations, including the GUI's transaction details dialog and the "vsize" result in many RPC results, transaction virtual sizes may not account for an unusually high number of sigops (ie, as determined by the -bytespersigop policy). This could result in reporting a lower virtual size than is actually used for mempool or mining purposes.

• Refactor DatacarrierBytes & CalculateExtraTxWeight to use CTxUndo
• rpc_sign_show_fees
• TxToUniv "vsize" should be able to use undo data
• MempoolTxsToJSON: need to generate fake undo data
• decoderawtransaction: ???
• decodepsbt: ???
• TxToJSON/getrawtransaction: should be able to figure out from undo data OR mempool
• doc & tests: handle vsize possibly being missing (pruned blocks)
• wallet/gettransaction: should be able to figure out from undo data OR mempool
• bitcoin-tx/OutputTxJSON: omit vsize & doc???
• rest_tx: should be able to figure out from undo data OR mempool