Add missing standard library includes for self-sufficient headers

Fixes builds with newer GCC/libstdc++ that no longer provide <cstdint>,
<cstring>, <cfloat>, <memory>, <algorithm> etc. transitively. Also
disambiguates visit<> calls in taxonomy.h with the full namespace and
casts the character value in IfcCharacterDecoder to uint32_t to silence
ambiguous overload warnings.

src/ifcgeom/kernels/opencascade/clash_utils.cpp

@@ -1,5 +1,7 @@
 #include "clash_utils.h"
 #include <cassert>
+#include <cstdint>
+#include <cfloat>
 
 #define GU_CULLING_EPSILON_RAY_TRIANGLE FLT_EPSILON*FLT_EPSILON
 #define PX_MAX_F32 3.4028234663852885981170418348452e+38F