[clang-format] Do not insert space before closing brace in ObjC dict literal

Summary:
Previously, `clang-format` would sometimes insert a space
before the closing brace in an Objective-C dictionary literal.

Unlike array literals (which obey `Style.SpacesInContainerLiterals`
to add a space after `[` and before `]`), Objective-C dictionary
literals currently are not meant to insert a space after `{` and before
`}`, regardless of `Style.SpacesInContainerLiterals`.

However, some constructs like `@{foo : @(bar)}` caused `clang-format`
to insert a space between `)` and `}`.

This fixes the issue and adds tests. (I understand the behavior is
not consistent between array literals and dictionary literals, but
that's existing behavior that's a much larger change.)

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

Reviewers: djasper, jolesiak, Wizard

Reviewed By: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D44816

llvm-svn: 328627