[clang-tidy][NFC] Improve naming convention in...

[clang-tidy][NFC] Improve naming convention in google-readability-avoid-underscore-in-googletest-name

According to the Google docs, the convention is
TEST(TestSuiteName, TestName). Apply that convention to the
source code, test and documentation of the check.

Differential Revision: https://reviews.llvm.org/D146713