[nostaliga/core] Add Drawer system and make ImGui use configurable

src/nostalgia/core/gfx.hpp

@@ -76,6 +76,10 @@ ox::Error initGfx(Context *ctx) noexcept;
 
 ox::Error shutdownGfx(Context *ctx) noexcept;
 
+void addCustomDrawer(Context *ctx, Drawer *cd) noexcept;
+
+void removeCustomDrawer(Context *ctx, Drawer *cd) noexcept;
+
 [[nodiscard]]
 int getScreenWidth(Context *ctx) noexcept;