[ast-builder] Add constructor functions for type params
[ast-builder] Add constructor functions for type params

Summary: Makes constructing type params less verbose.

Reviewed By: gkz

Differential Revision: D29736981

fbshipit-source-id: 07ee1dfb51f448fa490e2f1c1a25103d01bd285e

mroch/flow,mroch/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,facebook/flow,mroch/flow