Use the short form of an opcode in ILGenerator.EmitWriteLine. (dotnet…

…#59836)

`ILGenerator.Emit(short)` does not use short forms if applicable; only the int overload does, but here we can directly use `ldarg.0`.

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/ILGenerator.cs

@@ -1210,7 +1210,7 @@ public virtual void EmitWriteLine(FieldInfo fld)
             }
             else
             {
-                Emit(OpCodes.Ldarg, (short)0); // Load the this ref.
+                Emit(OpCodes.Ldarg_0); // Load the this ref.
                 Emit(OpCodes.Ldfld, fld);
             }
             Type[] parameterTypes = new Type[1];