The `__future__` we relied on is now, where the 3 specific things are
all included [since Python 3.0](https://docs.python.org/3/library/__future__.html):
* absolute_import
* print_function
* unicode_literals
* division
These import statements are no-ops and are no longer necessary.
• There is now one access note success remark and fix-it per declaration, not per attribute/modifier.
• Failure remarks have been rephrased to better emphasize the cause of the failure.
• The wording of other access note remarks and notes have been changed to follow a similar formula.
This commit adds an ObjCReason::ExplicitlyObjCByAccessNote value which diagnoses invalid uses, but using remarks instead of errors so that the failures don’t block builds even with -warnings-as-errors enabled.
This commit also adds annotations to attr/attr_objc.swift to generate a ton of access note test cases from it. In this commit, many of these test cases don’t pass yet. Subsequent commits will fix these bugs.
