Minimize usages of jet.* in Java code: this will help in migration of jet.* to
package kotlin. Since tests will work with fq names instead of Class<?>
instances from now on, ClassLoaderIsolationUtil is useless now (except for one
unrelated method, which was moved to CodegenTestUtil)
LoadCompiledKotlin and DescriptorSerialization tests should cover this.
KotlinClassAnnotationTest should only test that the correct annotation is
written
This helps to get rid of "repeated class_name" field in Package protobuf
message. DescriptorFinder in resolve.java uses PSI to find all classes in a
package, and the finder for built-ins just reads .kotlin_class_names file
Alexander Udalov