[@types/braintree] Added validation error types. (#37148)
[@types/braintree] Added validation error types. (#37148)

* Added validation error types.

* Removed presumably private interfaces.

georgemarshall/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,mcliment/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped