Add IWYU pragmas to library/cpp/testing/gtest/gtest.h, remove from ignore list

commit_hash:78d100f33169991cd5dd97d46b7f816695da7a50

Author: vadim-xd

library/cpp/testing/gtest/gtest.h

@@ -1,11 +1,13 @@
 #pragma once
 
+// IWYU pragma: begin_exports
 #include <library/cpp/testing/gtest/matchers.h>
 
 #include <library/cpp/testing/gtest_extensions/gtest_extensions.h>
 
 #include <gtest/gtest.h>
 #include <gmock/gmock.h>
+// IWYU pragma: end_exports
 
 #include <optional>
 #include <string_view>