Previously, packages `java.lang` and `kotlin.jvm` were imported on JVM
by default on the same rights, causing problems when the same classifier
existed both in `java.lang` and `kotlin.jvm`. Since the only known case
of such conflict were type aliases to JVM classes, the corresponding
classes (expansions of those type aliases) were manually excluded from
default imports. This made the code in DefaultImportProvider complicated
and resulted in multiple problems, regarding both correctness and
performance (see 82364ad3e5, a9f2f5c7d0, dd3dbda719).
This change adds a new concept, a "low priority import", and treats
`java.lang` as such. Since these imports are now separated from the rest
of default imports in LazyImportScope via secondaryClassImportResolver,
conflicts between classifiers are handled naturally: the one from
`kotlin.jvm` always wins (unless the one from `java.lang` is imported
explicitly, of course). This approach is simpler, safer and does not
require any memory to cache anything.
Skip ResolveToJava.kt test for javac-based resolve; it now fails because
of a weird issue which I didn't have time to investigate (this is OK
because it's a corner case of an experimental functionality)
