Codechange: Move dropdown and slider out of widgets directory. (#12403)

Also shuffle headers to place widget includes near end.

This leaves the widgets directory solely for defining Widget IDs.

src/screenshot_gui.cpp

@@ -11,10 +11,14 @@
 #include "window_func.h"
 #include "window_gui.h"
 #include "screenshot.h"
-#include "widgets/screenshot_widget.h"
-#include "table/strings.h"
 #include "gfx_func.h"
 
+#include "widgets/screenshot_widget.h"
+
+#include "table/strings.h"
+
+#include "safeguards.h"
+
 struct ScreenshotWindow : Window {
 	ScreenshotWindow(WindowDesc *desc) : Window(desc)
 	{