Summary:
Xcode really sucks, per some discussion on e1577df1fd and https://developer.apple.com/library/content/technotes/tn2215/_index.html, if you use the headers phase, and mark headers in your static library as public, they will actually end up in the final package that's built and you can't submit to the app store! This changes our xcode setup to use a copy files phase instead.
I've also changed the header include path to be $(BUILT_PRODUCTS_DIR)/include, which is added to the include path by Xcode by default, so 3rd party libraries should not be impacted by these changes anymore.
Reviewed By: mkonicek
Differential Revision: D4291607
fbshipit-source-id: 969b9ebcbeb8161f85427f8c429e198d9d0fae30
59407f3660