[clang-format][NFC] Clean up unit tests

This patch adds a verifyNoChange macro to verify code that won't
change after being formatted. (The code will not be messed up before
being formatted.) It then replaces EXPECT_EQ with verifyFormat
wherever applicable so that the code will be messed up before being
formatted. When the replacement fails the unit test, verifyFormat is
replaced with verifyNoChange.

Differential Revision: https://reviews.llvm.org/D153109