Cleanup includes

Reorder a few includes, include "position.h" where it was previously missing
and apply include-what-you-use suggestions. Also make the order of the includes
consistent, in the following way:

1. Related header (for .cpp files)
2. A blank line
3. C/C++ headers
4. A blank line
5. All other header files

closes https://github.com/official-stockfish/Stockfish/pull/4763
fixes https://github.com/official-stockfish/Stockfish/issues/4707

No functional change

src/thread.h

@@ -21,14 +21,16 @@
 
 #include <atomic>
 #include <condition_variable>
+#include <cstddef>
+#include <cstdint>
 #include <mutex>
-#include <thread>
 #include <vector>
 
 #include "movepick.h"
 #include "position.h"
 #include "search.h"
 #include "thread_win32_osx.h"
+#include "types.h"
 
 namespace Stockfish {