[clang-format/ObjC] Prohibit breaking after a bracket opening ObjC method expression

Summary:
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

llvm-svn: 336519