Implement IME input support

Refactor TextBox control to handle IME composition with inline preview and input panels at cursor.
Toggle IME composition mode only when player enters or exits input UIs. IME must remain disabled during gameplay.
Standard non-IME text input should remain unchanged and behave the same as before. The IME pathway is only activated when user has a suitable provider installed to OS and has enabled IME typing.
Still requires some testing and no doubt bugfix before this is ready for live builds.

Assets/Scripts/Game/DaggerfallUI.cs

@@ -392,6 +392,9 @@ void Start()
                 pixelFontMaterial.EnableKeyword(KeyWords.MacOSX);
                 sdfFontMaterial.EnableKeyword(KeyWords.MacOSX);
             }
+
+            // Reset IME composition mode to default at startup
+            Input.imeCompositionMode = IMECompositionMode.Auto;
         }
 
         void Update()
@@ -452,9 +455,6 @@ void OnGUI()
 
                 if (Event.current.keyCode != KeyCode.None)
                     lastKeyCode = Event.current.keyCode;
-
-                if (lastCharacterTyped > 255)
-                    lastCharacterTyped = (char)0;
             }
 
             if (processHotkeys)