Fix backslash operator to use SCALAR context for most operands

The backslash operator (\) was evaluating all non-\& operands in LIST
context, which caused issues when creating references to constant subs
or other expressions that return scalars.

For example, \PVBM where PVBM is a constant sub would evaluate PVBM()
in LIST context, returning a RuntimeList, then call createReference() on
it which throws 'create reference of list not implemented'.

This fix changes the backslash operator to evaluate most operands in
SCALAR context (the natural context for creating a reference to a value).
LIST context is only used for actual list-producing operations like @ and %
variables, or explicit ListNodes.

This fixes the remaining failures in t/op/bop.t related to references.

Progress on t/op/bop.t: Now passes 313 out of 522 tests (59%)

Author: fglock

src/main/java/org/perlonjava/codegen/EmitOperator.java

@@ -893,7 +893,15 @@ static void handleCreateReference(EmitterVisitor emitterVisitor, OperatorNode no
                     node.operand.accept(emitterVisitor.with(RuntimeContextType.LIST));
                 }
             } else {
-                node.operand.accept(emitterVisitor.with(RuntimeContextType.LIST));
+                // For most cases, evaluate in SCALAR context to get a reference to the value
+                // Only use LIST context for actual list-producing operations
+                int contextType = RuntimeContextType.SCALAR;
+                if (node.operand instanceof ListNode || 
+                    (node.operand instanceof OperatorNode op && 
+                     (op.operator.equals("@") || op.operator.equals("%")))) {
+                    contextType = RuntimeContextType.LIST;
+                }
+                node.operand.accept(emitterVisitor.with(contextType));
                 emitterVisitor.ctx.mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL,
                         "org/perlonjava/runtime/RuntimeBase",
                         "createReference",