[clang-format] Disable AlwaysBreakBeforeMultilineStrings in Google style for Objective-C

Contributed by @stephanemoore.

Reviewers: benhamilton, jolesiak, djasper

Reviewed By: benhamilton

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D47393

llvm-svn: 334739