Replace `LuaPictureBox` prop init with constructor

src/BizHawk.Client.EmuHawk/tools/Lua/Libraries/FormsLuaLibrary.cs

@@ -305,7 +305,7 @@ namespace BizHawk.Client.EmuHawk
 				return 0;
 			}
 
-			var pictureBox = new LuaPictureBox { TableHelper = _th };
+			LuaPictureBox pictureBox = new(_th);
 			form.Controls.Add(pictureBox);
 			const string FUNC_NAME = "forms.pictureBox";
 			ProcessPositionArguments(x: x, y: y, pictureBox, functionName: FUNC_NAME);

src/BizHawk.Client.EmuHawk/tools/Lua/LuaCanvas.cs

@@ -56,7 +56,7 @@ namespace BizHawk.Client.EmuHawk
 				}
 			}
 
-			luaPictureBox = new LuaPictureBox
+			luaPictureBox = new(_th)
 			{
 				Image = Properties.Resources.LuaPictureBox,
 				Location = new Point(0, 0),
@@ -65,7 +65,6 @@ namespace BizHawk.Client.EmuHawk
 				Size = new Size(100, 50),
 				SizeMode = PictureBoxSizeMode.AutoSize,
 				TabIndex = 0,
-				TableHelper = _th,
 				TabStop = false
 			};
 			Controls.Add(luaPictureBox);

src/BizHawk.Client.EmuHawk/tools/Lua/LuaPictureBox.cs

@@ -17,7 +17,7 @@ namespace BizHawk.Client.EmuHawk
 		private readonly Dictionary<Color, SolidBrush> _solidBrushes = new Dictionary<Color, SolidBrush>();
 		private readonly Dictionary<Color, Pen> _pens = new Dictionary<Color, Pen>();
 
-		internal NLuaTableHelper TableHelper { get; set; }
+		private readonly NLuaTableHelper TableHelper;
 
 		private SolidBrush GetBrush([LuaColorParam] object color)
 			=> _solidBrushes.GetValueOrPutNew1(TableHelper.ParseColor(color));
@@ -29,9 +29,10 @@ namespace BizHawk.Client.EmuHawk
 		private Color? _defaultBackground;
 		private Color? _defaultTextBackground = Color.FromArgb(128, 0, 0, 0);
 
-		public LuaPictureBox()
+		public LuaPictureBox(NLuaTableHelper tableHelper)
 		{
 			Image = new Bitmap(Width, Height);
+			TableHelper = tableHelper;
 		}
 		
 		public void LuaResize(int width, int height)