improve readInlineData flow type
improve readInlineData flow type

Summary: Simplifies the typing by using an overload instead of `$Call` magic. This now also means that the we can properly infer the return value from the passed in argument type.

Reviewed By: josephsavona

Differential Revision: D15906579

fbshipit-source-id: d34ce24c7a0b15d4c5be8722e89e703434ff9d96

cpojer/relay,xuorig/relay,kassens/relay,wincent/relay,facebook/relay,kassens/relay,xuorig/relay,wincent/relay,kassens/relay,cpojer/relay,voideanvalue/relay,wincent/relay,josephsavona/relay,wincent/relay,xuorig/relay,atxwebs/relay,facebook/relay,josephsavona/relay,facebook/relay,yungsters/relay,atxwebs/relay,kassens/relay,yungsters/relay,atxwebs/relay,facebook/relay,zpao/relay,josephsavona/relay,xuorig/relay,iamchenxin/relay,atxwebs/relay,voideanvalue/relay,facebook/relay,voideanvalue/relay,cpojer/relay,kassens/relay,voideanvalue/relay,iamchenxin/relay,xuorig/relay,voideanvalue/relay,facebook/relay,voideanvalue/relay,xuorig/relay,iamchenxin/relay,yungsters/relay,zpao/relay,kassens/relay,wincent/relay,iamchenxin/relay,wincent/relay,cpojer/relay,zpao/relay