Move the stub test from initialize_final_stubs() to test/hotspot/gtest

When doing task JDK-8287325, I noticed that some stub routine tests are done inside function initialize_final_stubs(). See the code https://github.com/openjdk/jdk/blob/master/src/hotspot/share/runtime/stubRoutines.cpp#L325-L404
The test runs every time the debug VM is started.

I thought it's a usual convention that we'd better not to do functional tests on startup. Besides, we have the existing gtest framework for testing internal C++ modules.

Hence, I think it's worthing moving the stub test from initialize_final_stubs() to test/hotspot/gtest.