Summary:
This diff adds a new `js1` script `js1 build viewconfigs` which will generate the view configs for generated components in xplat/js
Note that the view configs are not currently valid so I'm not checking them in or adding them to a test, that work will follow
Reviewed By: TheSavior
Differential Revision: D15239656
fbshipit-source-id: d15776f36a7d7684f50beafd783bccb02352afc0
