[clang-format] fix regression recognizing casts in Obj-C calls

Summary:
r373922 added checks for a few tokens that, following an `)` make it
unlikely that the `)` is the closing paren of a cast expression. The
specific check for `tok::l_square` there introduced a regression for
casts of Obj-C calls, like:
```
(cast)[func arg]
```
From the tests added in r373922, I believe the `tok::l_square` case is added to
capture the case where a non-cast `)` is directly followed by an
attribute specifier, like:
```
int f(int x) [[noreturn]];
```

I've specialized the code to look for such attribute specifier instead
of `tok::l_square` in general. Also, I added a regression test and moved
the test cases added in r373922 to an already existing place documenting
other instances of historically misidentified casts.

Reviewers: MyDeveloperDay

Reviewed By: MyDeveloperDay

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D69164

llvm-svn: 375247