8159970: javac, JLS8 18.2.4 is not completely implemented by the compiler
Reviewed-by: mcimadamore

8076543: Add @modules as needed to the langtools tests
Reviewed-by: jjg, shurailine

7006109: Add test library to simplify the task of writing automated type-system tests
Summary: Types.java needs to be more stress-tested
Reviewed-by: jjg