[clang-format] Refine structured binding detection

Summary:
Revision r356575 had the unfortunate consequence that now clang-format never
detects an ObjC call expression after &&.

This patch tries harder to distinguish between C++17 structured bindings and
ObjC call expressions and adds a few regression tests.

Reviewers: klimek

Reviewed By: klimek

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D59774

llvm-svn: 356928