[Ty][Debug] Extend json printing to symbols
[Ty][Debug] Extend json printing to symbols

Summary:
Extend Ty json printing to symbols.

This change will help print a more comprehensive Ty description with changes
that are coming later on `type-at-pos --json`.

Reviewed By: samwgoldman

Differential Revision: D7778306

fbshipit-source-id: a993fb0edef1fbce62333eee8e119de063e59f4c

JonathanUsername/flow,claudiopro/flow,mroch/flow,nmote/flow,mroch/flow,facebook/flow,popham/flow,nmote/flow,gabelevi/flow,samwgoldman/flow,AgentME/flow,samwgoldman/flow,facebook/flow,popham/flow,popham/flow,nmote/flow,JonathanUsername/flow,JonathanUsername/flow,nmote/flow,JonathanUsername/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,jamesgpearce/flow,AgentME/flow,nmote/flow,AgentME/flow,mroch/flow,facebook/flow,jamesgpearce/flow,samwgoldman/flow,AgentME/flow,jamesgpearce/flow,claudiopro/flow,JonathanUsername/flow,facebook/flow,nmote/flow,popham/flow,mroch/flow,gabelevi/flow,popham/flow,JonathanUsername/flow,claudiopro/flow,jamesgpearce/flow,mroch/flow,JonathanUsername/flow,gabelevi/flow,claudiopro/flow,jamesgpearce/flow,claudiopro/flow,facebook/flow,samwgoldman/flow,gabelevi/flow,mroch/flow,gabelevi/flow,jamesgpearce/flow,gabelevi/flow,popham/flow,samwgoldman/flow,gabelevi/flow,mroch/flow,facebook/flow,popham/flow,AgentME/flow,nmote/flow,jamesgpearce/flow