WARNING: This is not like all the other extension traits.
Because of the use of generics on various `Transaction` methods it is
not easily possible to use the `define_extension_trait` macro.
Manually create the extension traits (public and private) for the
`Transaction` type. This is quite ugly but c'est la vie
(Includes two in the `transaction` module and one in the
`consensus_validation` module.)
98383a0fbe