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)
Remove references to "out/production/builtins", since those built-ins are
compiled by the bootstrap compiler, whereas we want to test built-ins compiled
by the new (working copy) compiler
'builtins' will be used for platform-independent core built-in definitions,
'runtime.jvm' for things that should be present at runtime in order for Kotlin
code to execute correctly on JVM
ProgressionUtil goes to 'builtins' right now because progression iterators
depend on it, but should be rewritten to Kotlin later
Andrey Breslav