Create `function_body_any` mapper
Create `function_body_any` mapper

Summary: Abstract the real function body mapper to its own function. I wanted to replace the existing `function_body` mapper but saw that it was used elsewhere so instead I went with a new function that "preceeds" it, as it were.

Reviewed By: gabelevi

Differential Revision: D8801260

fbshipit-source-id: 69ec9a12451ecc934b13845be5484f615e3e336a

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