misc optimizations for showing lookup with many elements:

- using ContainerUtil.toArray
- cheaper checks of relevance to Java-specific weighers
- avoid expensive Class#isInstanceOf of LookupElement#as using:
     * LookupItem#from with explicit instanceof LookupItem (caring of LookupElementDecorator)
     * isCaseSensitive introduced to LookupElement

java/java-impl/src/com/intellij/codeInsight/completion/JavaCompletionUtil.java

@@ -789,9 +789,8 @@ public class JavaCompletionUtil {
       return typed.getType();
     }
 
-
     final PsiType qualifierType = getPsiType(element.getObject());
-    final LookupItem lookupItem = element.as(LookupItem.class);
+    final LookupItem lookupItem = LookupItem.from(element);
     if (lookupItem != null) {
       final Object o = lookupItem.getAttribute(LookupItem.TYPE);
       if (o instanceof PsiType) {