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/ifcparse/character_decoder.cpp

@@ -288,7 +288,7 @@ namespace {
                 if (character >= 0x20 && character <= 0x7e) {
                     stream.put((char)character);
                 } else {
-                    stream << "\\u" << character;
+                    stream << "\\u" << static_cast<uint32_t>(character);
                 }
             });
             return stream.str();