Add a util for parsing the rpc._getTransaction

[kalepail]

Is your feature request related to a problem? Please describe.
Often you will use a backend service to submit your transactions and then forward the raw response back to your frontend. This leaves you in a state needing to parse that raw JSON back into some form. This is tedious, error prone, and unnecessary given these utils already exist privately in the JS SDK.

Describe the solution you'd like
We have utils for parsing raw simulation, we should also provide a util for parsing a raw transaction get request.

Describe alternatives you've considered
Writing it by hand. Manually converting the xdr to it's relevant types. Ew.