Use two-way mapping for mnemonics -> opcodes

libs/UIX.Asm/Models/SyntaxModels.cs

@@ -1,6 +1,7 @@
 using Microsoft.Iris.Markup;
 using System.Collections.Generic;
 using System.Linq;
+using System.Text;
 
 namespace Microsoft.Iris.Asm.Models;
 
@@ -9,6 +10,15 @@ public interface IImport { }
 
 public record Instruction(string Mnemonic, IEnumerable<Operand> Operands) : IBodyItem
 {
+    public Instruction(OpCode opCode, OperationType? operationType, IEnumerable<Operand> Operands)
+        : this(LexerMaps.GetMnemonic(opCode, operationType), Operands)
+    {
+    }
+    public Instruction(OpCode opCode, IEnumerable<Operand> Operands)
+        : this(opCode, null, Operands)
+    {
+    }
+
     public OpCode OpCode => LexerMaps.MnemonicToOpCode(Mnemonic);
     public OperationType? OperationType => LexerMaps.TryOperationMnemonicToType(Mnemonic);
 
@@ -27,5 +37,13 @@ public record Operand(object Value, string Content = null)
 
 public record Program(IEnumerable<IImport> Imports, IEnumerable<IBodyItem> Body)
 {
-    public override string ToString() => string.Join("\r\n", Imports.Select(i => i.ToString()).Concat(Body.Select(b => b.ToString())));
+    public override string ToString()
+    {
+        StringBuilder sb = new();
+
+        sb.AppendJoin("\r\n", Imports.Select(i => i.ToString()));
+        sb.AppendJoin("\r\n", Body.Select(b => b.ToString()));
+
+        return sb.ToString();
+    }
 }