Specifically, the case when not all parts of a multifile class are
annotated with `@JvmSynthetic`. Report the error on the
`@JvmMultifileClass` annotation instead of the package directive,
because the latter is difficult to find via IR. This fixes the test
FirLightTreeDiagnosticsTestWithJvmIrBackendGenerated.MultifileClasses.testJvmSynthetic.
#KT-59586
We are going to deprecate `WITH_RUNTIME` directive. The main reason
behind this change is that `WITH_STDLIB` directive better describes
its meaning, specifically it will add kotlin stdlib to test's classpath.
Alexander Udalov