Add format checking

[sublimator]

The primary client of this module is RippleAPI which checks/enforces its own schema, however it would still be useful to add per TransactionType format checking to encodeForSigning and encodeForMultiSigning

[intelliot]

Should we just throw if the format check fails?

[sublimator]

I would

[sublimator]

I think @wilsonianb might be using it for validator manifests, which have no TransactionType/LedgerEntryType so keep that in mind.

[sublimator]

So probably you could get away with full format checking if LedgerEntryType/TransactionType field is in the object, $somehow detect a validator manifest and handle accordingly, otherwise require at least one serialized field (https:/ripple/ripple-binary-codec/blob/master/src/enums/definitions.json#L40)

[intelliot]

Replaced by XRPLF/xrpl.js#1807