Refactor Stats Array

* Limit use of `StatsEntry` wrapper to arithmetic types
* Generalize `Stats` to `MultiArray` by discarding the template parameter `D`
* Allow `MultiArray::fill` to take any type assignable to element type
* Remove now-unused operator overloads on `StatsEntry`

closes https://github.com/official-stockfish/Stockfish/pull/5750

No functional change

src/movepick.cpp

@@ -22,6 +22,7 @@
 #include <limits>
 
 #include "bitboard.h"
+#include "misc.h"
 #include "position.h"
 
 namespace Stockfish {