Summary: public
Dictionary literals are normally implemented using
`+dictionaryWithObjects:forKeys:count:` but were modeled as
`+dictionaryWithObjectsAndKeys:`
In particular, `@{@"aaa": nil}` would trigger a sentinel error instead of an NPE.
This models dictionary literals as a special infer builtin that the backend
interprets so as to give NPEs when passed nil objects or keys.
Reviewed By: dulmarod
Differential Revision: D2550039
fb-gh-sync-id: 1a10656