Use BitSet to represent JVM IsHllInit values

It would be really inefficient to use an array to record whether the hll
statevar is init when only one bit is needed (per lexical), especially
when there are a large amount of lexicals. Record in a BitSet instead.

src/vm/jvm/runtime/org/perl6/nqp/runtime/CallFrame.java

@@ -1,5 +1,6 @@
 package org.perl6.nqp.runtime;
 
+import java.util.BitSet;
 import java.util.HashMap;
 
 import org.perl6.nqp.sixmodel.InvocationSpec;
@@ -149,7 +150,7 @@ public CallFrame(ThreadContext tc, CodeRef cr) {
                 case 2:
                     if (cr.oLexState == null) {
                         cr.oLexState = new SixModelObject[sci.oLexStatic.length];
-                        cr.oLexStateIsHllInit = new boolean[sci.oLexStatic.length];
+                        cr.oLexStateIsHllInit = new BitSet(sci.oLexStatic.length);
                         this.stateInit = true;
                     }
                     if (cr.oLexState[i] == null)

src/vm/jvm/runtime/org/perl6/nqp/runtime/CodeRef.java

@@ -1,6 +1,8 @@
 package org.perl6.nqp.runtime;
 import java.lang.invoke.MethodHandle;
 
+import java.util.BitSet;
+
 import org.perl6.nqp.sixmodel.SixModelObject;
 
 /**
@@ -41,7 +43,7 @@ public class CodeRef extends SixModelObject {
     /**
      * Has the given statevar been assigned a value by the HLL?
      */
-    public boolean[] oLexStateIsHllInit;
+    public BitSet oLexStateIsHllInit;
 
     /**
      * The (human-readable) name of the code-ref (not in staticInfo as a