[clang-format/ObjC] Prohibit breaking after a bracket opening ObjC method expression
Don't break after a "[" opening an ObjC method expression.
Tests are added in D48719 where formatting is improved (to avoid adding and changing tests immediately).
Reviewers: benhamilton, klimek
Reviewed By: benhamilton
Subscribers: acoomans, cfe-commits
Differential Revision: https://reviews.llvm.org/D48718