starius / btcd / 37355032955

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txscript: reject SIGHASH_SINGLE signing without a matching output

When SIGHASH_SINGLE has no output corresponding to the input being
signed, legacy signing uses the constant hash one and segwit v0 signing
commits to no outputs. These signatures can allow funds to be
redirected.

Reject this case in RawTxInSignature and RawTxInWitnessSignature with
ErrInvalidSigHashSingleIndex, including when ANYONECANPAY is set.
Their callers inherit the protection; multisig signing omits refused
signatures through its existing error handling. The check masks the
hash type with sigHashMask (0x1f) like the sighash code, where Core
masks with 3; the two agree for the standard hash types.

Leave sighash calculation unchanged to preserve consensus verification.
Taproot signing already rejects this case.

Add regression coverage for P2PKH, bare multisig, P2WPKH and P2TR across
the six standard explicit sighash types, checking both missing-output
rejection and successful signing of supported combinations.

Port of Bitcoin Core PR bitcoin/bitcoin#35984:
https://github.com/bitcoin/bitcoin/pull/35984

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