[jvm] Boost size of multi-dispatch cache

This copies what was done for (old multi-dispatch cache of) MoarVM with
MoarVM/MoarVM@99bf383cb1

src/vm/jvm/runtime/org/perl6/nqp/sixmodel/reprs/MultiCacheInstance.java

@@ -8,7 +8,7 @@
 
 public class MultiCacheInstance extends SixModelObject {
     private static final int MD_CACHE_MAX_ARITY = 4;
-    private static final int MD_CACHE_MAX_ENTRIES = 16;
+    private static final int MD_CACHE_MAX_ENTRIES = 32;
     private static final int MD_CACHE_INT = 1;
     private static final int MD_CACHE_NUM = 2;
     private static final int MD_CACHE_STR = 3;