Open packages for reflection by JUnit (#539 / #597)

JUnit (more precisely the module `org.junit.platform.commons`)
needs to reflectively access Pioneer packages. Since some classes
aren't public, this fails with an `InaccessibleObjectException` if
Pioneer is placed on the module path. To fix this, the packages
must be opened.

Furthermore, this change fixes a mistake from #415 and exports the
new package `org.junitpioneer.jupiter.cartesian`.

Closes: #539
PR: #597

src/main/module/module-info.java

@@ -6,8 +6,14 @@
 
 	exports org.junitpioneer.vintage;
 	exports org.junitpioneer.jupiter;
+	exports org.junitpioneer.jupiter.cartesian;
 	exports org.junitpioneer.jupiter.params;
 
+	opens org.junitpioneer.vintage to org.junit.platform.commons;
+	opens org.junitpioneer.jupiter to org.junit.platform.commons;
+	opens org.junitpioneer.jupiter.cartesian to org.junit.platform.commons;
+	opens org.junitpioneer.jupiter.params to org.junit.platform.commons;
+
 	provides org.junit.platform.launcher.TestExecutionListener
 			with org.junitpioneer.jupiter.issue.IssueExtensionExecutionListener;
 	uses org.junitpioneer.jupiter.IssueProcessor;