Fix #9386: compilers failing to compile with LTO by using variants instead of new + unique_ptr

With std::variant all memory can be figured out at compile time, so the compiler needs to keep track of fewer elements. It also saves out a unique_ptr and its memory management, over a slight impact for resolving a setting.

src/table/settings/window_settings.ini

@@ -9,7 +9,7 @@
 
 [pre-amble]
 
-static const SettingTable _window_settings{
+static const SettingVariant _window_settings[] = {
 [post-amble]
 };
 [templates]