SCons: Move platform logo/run icon to export folder

Follow-up to #75932.
Since these icons are only used by the export plugin, it makes sense to
move them and generate the headers there.

The whole `detect.is_active()` logic seems to be a leftover from before
times, as far back as 1.0-stable it already wasn't used for anything.

So I'm removing it and moving the export icon generation to
`platform_methods`, where it makes more sense.

platform/uwp/export/export_plugin.cpp

@@ -30,7 +30,7 @@
 
 #include "export_plugin.h"
 
-#include "../logo_svg.gen.h"
+#include "logo_svg.gen.h"
 
 #include "editor/editor_scale.h"
 #include "editor/editor_settings.h"