Move UArraysKt into kotlin.collections.unsigned package

Provide UArraysKt class in kotlin.collections for binary compatibility
instead of removed multipart facade class. It contains only non-inline
functions of the latter.

libraries/stdlib/jvm/java9/module-info.java

@@ -2,6 +2,7 @@ module kotlin.stdlib {
     exports kotlin;
     exports kotlin.annotation;
     exports kotlin.collections;
+    exports kotlin.collections.unsigned;
     exports kotlin.comparisons;
     exports kotlin.concurrent;
     exports kotlin.contracts;