[hack] Allow Shapes::idx(...) default to be the subtype of field type
[hack] Allow Shapes::idx(...) default to be the subtype of field type

Summary: Looks like currently it must be equal or supertype - changing it to mimic the behaviour of Indexish idx(...) - we allow any type, and reflect it in returning Tunresolved.

Reviewed By: dlreeves

Differential Revision: D2627515

fb-gh-sync-id: 78ad60c67de794e55bfd9855fb9a7796ac2d0d87

AprilArcus/flow,gabelevi/flow,shiftcars/flow,jdelStrother/flow,jgrund/flow,chenglou/flow,nmote/flow,claudiopro/flow,JonathanUsername/flow,gabelevi/flow,jdelStrother/flow,popham/flow,popham/flow,popham/flow,samwgoldman/flow,TiddoLangerak/flow,JonathanUsername/flow,MichaelDeBoey/flow,cesarandreu/flow,AprilArcus/flow,jeffmo/flow,AgentME/flow,ForbesLindesay/flow,mroch/flow,graue/flow,popham/flow,fletcherw/flow,AgentME/flow,fletcherw/flow,ylu1317/flow,fletcherw/flow,jeffmo/flow,facebook/flow,jeffmo/flow,fletcherw/flow,chenglou/flow,shiftcars/flow,jamesgpearce/flow,popham/flow,MichaelDeBoey/flow,facebook/flow,TiddoLangerak/flow,JonathanUsername/flow,facebook/flow,shiftcars/flow,mroch/flow,graue/flow,TiddoLangerak/flow,nmote/flow,cesarandreu/flow,MichaelDeBoey/flow,d14b3l/flow,jgrund/flow,samwgoldman/flow,shiftcars/flow,jgrund/flow,OCamlPro/flow,d14b3l/flow,mroch/flow,cesarandreu/flow,AgentME/flow,AprilArcus/flow,facebook/flow,jgrund/flow,AprilArcus/flow,samwgoldman/flow,jeffmo/flow,jamesgpearce/flow,claudiopro/flow,graue/flow,jamesgpearce/flow,popham/flow,JonathanUsername/flow,d14b3l/flow,claudiopro/flow,shiftcars/flow,OCamlPro/flow,fletcherw/flow,JonathanUsername/flow,nmote/flow,ForbesLindesay/flow,MichaelDeBoey/flow,OCamlPro/flow,samwgoldman/flow,mroch/flow,facebook/flow,nmote/flow,facebook/flow,gabelevi/flow,JonathanUsername/flow,chenglou/flow,ylu1317/flow,jamesgpearce/flow,gabro/flow,samwgoldman/flow,jdelStrother/flow,gabelevi/flow,ylu1317/flow,jgrund/flow,shiftcars/flow,TiddoLangerak/flow,jgrund/flow,gabro/flow,ForbesLindesay/flow,gabro/flow,fletcherw/flow,cesarandreu/flow,gabro/flow,jeffmo/flow,AgentME/flow,mroch/flow,samwgoldman/flow,d14b3l/flow,OCamlPro/flow,jamesgpearce/flow,claudiopro/flow,samwgoldman/flow,claudiopro/flow,facebook/flow,chenglou/flow,nmote/flow,jdelStrother/flow,graue/flow,graue/flow,AprilArcus/flow,chenglou/flow,nmote/flow,gabro/flow,popham/flow,jeffmo/flow,gabro/flow,JonathanUsername/flow,chenglou/flow,gabelevi/flow,ForbesLindesay/flow,mroch/flow,jdelStrother/flow,ylu1317/flow,jamesgpearce/flow,jdelStrother/flow,AprilArcus/flow,TiddoLangerak/flow,mroch/flow,jamesgpearce/flow,graue/flow,d14b3l/flow,ForbesLindesay/flow,gabelevi/flow,ForbesLindesay/flow,gabelevi/flow,AgentME/flow,ylu1317/flow,nmote/flow,d14b3l/flow,MichaelDeBoey/flow