[PR] Add RegExp$matchResult.groups
[PR] Add RegExp$matchResult.groups

Summary:
Closes #6581.

cc mrkev re https://github.com/facebook/flow/issues/6581#issuecomment-404945277
Pull Request resolved: https://github.com/facebook/flow/pull/6604

Reviewed By: fishythefish

Differential Revision: D8889638

Pulled By: mrkev

fbshipit-source-id: 0d4e4765775d926d5cdaa3168296d87c18aff537

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