[clang-format/ObjC] Do not detect "[]" as ObjC method expression

[clang-format/ObjC] Do not detect "[]" as ObjC method expression

Summary:
The following C++ code was being detected by
`guessLanguage()` as Objective-C:

  #define FOO(...) auto bar = [] __VA_ARGS__;

This was because `[] __VA_ARGS__` is not currently detected as a C++
lambda expression (it has no parens or braces), so
`TokenAnnotator::parseSquare()` incorrectly treats the opening square
as an ObjC method expression.

We have two options to fix this:

1. Parse `[] __VA_ARGS__` explicitly as a C++ lambda
2. Make it so `[]` is never parsed as an Objective-C method expression

This diff implements option 2, which causes the `[` to be parsed
as `TT_ArraySubscriptLSquare` instead of `TT_ObjCMethodExpr`.

Note that when I fixed this, it caused one change in formatting
behavior, where the following was implicitly relying on the `[`
being parsed as `TT_ObjCMethodExpr`:

  A<int * []> a;

becomes:

  A<int *[]> a;

with `Style.PointerAlignment = Middle`.

I don't really know what the desired format is for this syntax; the
test was added by Janusz Sobczak and integrated by @djasper in
https://github.com/llvm-mirror/clang/commit/b511fe9818829d7ece0cc0b2ce1fbe04a1f0739a
.

I went ahead and changed the test for now.

Test Plan: New tests added. Ran tests with:
  % make -j12 FormatTests && ./tools/clang/unittests/Format/FormatTests

Fixes: https://bugs.llvm.org/show_bug.cgi?id=36248

Reviewers: djasper, jolesiak

Reviewed By: djasper

Subscribers: klimek, cfe-commits, djasper

Differential Revision: https://reviews.llvm.org/D45169

llvm-svn: 329070