[mlir] don't use magic numbers in IRNumbering.cpp

Bytecode versions have named constants that should be used instead of
magic numbers.

mlir/lib/Bytecode/Writer/IRNumbering.cpp

@@ -9,6 +9,7 @@
 #include "IRNumbering.h"
 #include "mlir/Bytecode/BytecodeImplementation.h"
 #include "mlir/Bytecode/BytecodeOpInterface.h"
+#include "mlir/Bytecode/Encoding.h"
 #include "mlir/IR/AsmState.h"
 #include "mlir/IR/BuiltinTypes.h"
 #include "mlir/IR/OpDefinition.h"
@@ -425,17 +426,20 @@ void IRNumberingState::number(Operation &op) {
 
   // Only number the operation's dictionary if it isn't empty.
   DictionaryAttr dictAttr = op.getDiscardableAttrDictionary();
-  // Prior to version 5, or when properties are not used, we need to number also
-  // the merged dictionary containing both the inherent and discardable
-  // attribute.
-  if (config.getDesiredBytecodeVersion() < 5 || !op.getPropertiesStorage())
+  // Prior to a version with native property encoding, or when properties are
+  // not used, we need to number also the merged dictionary containing both the
+  // inherent and discardable attribute.
+  if (config.getDesiredBytecodeVersion() <
+          bytecode::kNativePropertiesEncoding ||
+      !op.getPropertiesStorage()) {
     dictAttr = op.getAttrDictionary();
+  }
   if (!dictAttr.empty())
     number(dictAttr);
 
   // Visit the operation properties (if any) to make sure referenced attributes
   // are numbered.
-  if (config.getDesiredBytecodeVersion() >= 5 &&
+  if (config.getDesiredBytecodeVersion() >= bytecode::kNativePropertiesEncoding &&
       op.getPropertiesStorageSize()) {
     if (op.isRegistered()) {
       // Operation that have properties *must* implement this interface.