Move math and some file and data conversion files out from native to Common.

Buildfixing

Move some file util files

Buildfix

Move KeyMap.cpp/h to Core where they belong better.

libretro buildfix attempt

Move ini_file

More buildfixes

Common/Data/Convert/SmallDataConvert.cpp

@@ -0,0 +1,3 @@
+#include "Common/Data/Convert/SmallDataConvert.h"
+
+alignas(16) const float one_over_255_x4[4] = { 1.0f / 255.0f, 1.0f / 255.0f, 1.0f / 255.0f, 1.0f / 255.0f, };