Mesh: Add object name attribute to 3MF export

Export mesh object names as 'name' attribute in 3MF files according to
the 3MF specification. This allows downstream tools to identify objects
by their original FreeCAD names.

Changes:
- Moved Exporter::xmlEscape() to Base XMLTools::escapeXml() for shared XML entity escaping
- Update Writer3MF::AddMesh() to accept and output object names with default "" where no attribute will be added
- Updated all codepaths leading to 3mf exports to include the object name

src/Base/XMLTools.h

@@ -47,6 +47,7 @@ class BaseExport XMLTools
 public:
     static std::string toStdString(const XMLCh* const toTranscode);
     static std::basic_string<XMLCh> toXMLString(const char* const fromTranscode);
+    static std::string escapeXml(const std::string& input);
     static void initialize();
     static void terminate();