Create WindowColour enum for widget definition calls (#12722)

* Make MakeWidget* functions take enum colour

* Make windows A-D use WindowColour enum

* Make windows E-G use WindowColour enum

* Make windows I-M use WindowColour enum

* Make windows N-P use WindowColour enum

* Make windows R-S use WindowColour enum

* Make windows T use WindowColour enum

* Make windows V-W use WindowColour enum

src/openrct2-ui/windows/Dropdown.cpp

@@ -32,7 +32,7 @@ enum
 };
 
 static rct_widget window_dropdown_widgets[] = {
-    MakeWidget({ 0, 0 }, { 1, 1 }, WWT_IMGBTN, 0),
+    MakeWidget({ 0, 0 }, { 1, 1 }, WWT_IMGBTN, WindowColour::Primary),
     { WIDGETS_END },
 };