[clang-format/ObjC] Correctly annotate single-component ObjC method invocations

Summary:
Previously, clang-format's parser would fail to annotate the
selector in a single-component Objective-C method invocation with
`TT_SelectorName`. For example, the following:

  [foo bar];

would parse `bar` as `TT_Unknown`:

  M=0 C=1 T=Unknown S=0 B=0 BK=0 P=140 Name=identifier L=34 PPK=2
  FakeLParens= FakeRParens=0 II=0x559d5db51770 Text='bar'

This caused us to fail to insert a space after a closing cast rparen,
so the following:

  [((Foo *)foo) bar];

would format as:

  [((Foo *)foo)bar];

This diff fixes the issue by ensuring we annotate the selector
in a single-component Objective-C method invocation as
`TT_SelectorName`.

Test Plan: New tests added. Ran tests with:
  % make -j16 FormatTests && ./tools/clang/unittests/Format/FormatTests

Reviewers: djasper, jolesiak

Reviewed By: jolesiak

Subscribers: Wizard, klimek, hokein, cfe-commits

Differential Revision: https://reviews.llvm.org/D47028

llvm-svn: 332727