Some refactoring and cleanup (#1806)

* Use clang-tidy `misc-include-cleaner` for IWYU `#include` cleanup

* Use `std::optional<size_t>` instead of `ssize_t`

* Rename some functions in linkdefs.hpp

* Fix header order

include/gfx/pal_sorting.hpp

@@ -5,6 +5,7 @@
 
 #include <array>
 #include <optional>
+#include <stddef.h>
 #include <vector>
 
 #include "gfx/rgba.hpp"