Some TestNG tests require default constructors

Some tests use a non-standard pattern of static test methods, such that they have not hitherto required an instance object, and these tests do not have a default constructor that can be invoked by TestNG.

In TestNG 7, it is required that TestNG can create a test object: a test will now fail if a test object cannot be created, even if it is not required by the test method.

In core-libs, there are two such tests:

test/jdk/java/lang/Package/GetPackages.java
test/jdk/java/lang/StackWalker/Basic.java