add MetaProperty to ast-types
add MetaProperty to ast-types

Summary: Closes https://github.com/facebook/flow/pull/2459

Reviewed By: samwgoldman

Differential Revision: D3860227

Pulled By: mroch

fbshipit-source-id: 35287be31076b2cb54dce713250e89447d58eb6a

gabelevi/flow,ForbesLindesay/flow,MichaelDeBoey/flow,TiddoLangerak/flow,TiddoLangerak/flow,AprilArcus/flow,mroch/flow,chenglou/flow,chenglou/flow,samwgoldman/flow,facebook/flow,ylu1317/flow,mroch/flow,popham/flow,gabro/flow,AgentME/flow,jamesgpearce/flow,fletcherw/flow,fletcherw/flow,jamesgpearce/flow,AgentME/flow,JonathanUsername/flow,ylu1317/flow,mroch/flow,TiddoLangerak/flow,gabro/flow,jgrund/flow,facebook/flow,popham/flow,ylu1317/flow,facebook/flow,samwgoldman/flow,jamesgpearce/flow,AprilArcus/flow,chenglou/flow,claudiopro/flow,JonathanUsername/flow,jgrund/flow,jgrund/flow,samwgoldman/flow,gabelevi/flow,claudiopro/flow,AgentME/flow,gabelevi/flow,ylu1317/flow,jamesgpearce/flow,gabelevi/flow,gabelevi/flow,JonathanUsername/flow,popham/flow,facebook/flow,jamesgpearce/flow,mroch/flow,facebook/flow,nmote/flow,samwgoldman/flow,facebook/flow,AprilArcus/flow,gabro/flow,AgentME/flow,JonathanUsername/flow,chenglou/flow,chenglou/flow,gabro/flow,MichaelDeBoey/flow,MichaelDeBoey/flow,nmote/flow,gabro/flow,AprilArcus/flow,AprilArcus/flow,nmote/flow,jgrund/flow,nmote/flow,jamesgpearce/flow,chenglou/flow,fletcherw/flow,MichaelDeBoey/flow,ForbesLindesay/flow,JonathanUsername/flow,samwgoldman/flow,samwgoldman/flow,jgrund/flow,samwgoldman/flow,nmote/flow,popham/flow,nmote/flow,AgentME/flow,claudiopro/flow,claudiopro/flow,fletcherw/flow,TiddoLangerak/flow,ForbesLindesay/flow,fletcherw/flow,gabro/flow,AprilArcus/flow,MichaelDeBoey/flow,nmote/flow,facebook/flow,gabelevi/flow,popham/flow,mroch/flow,JonathanUsername/flow,ylu1317/flow,ForbesLindesay/flow,claudiopro/flow,JonathanUsername/flow,jamesgpearce/flow,jgrund/flow,mroch/flow,fletcherw/flow,TiddoLangerak/flow,ForbesLindesay/flow,ForbesLindesay/flow,popham/flow,gabelevi/flow,mroch/flow,popham/flow