Base: Add ComplexGeoData::centerOfGravity helper

This adds a simple quality of life helper returning center of gravity as
std::optional instead of C style method accepting reference and
returning bool to indicate method success.

src/App/ComplexGeoData.cpp

@@ -184,6 +184,17 @@ bool ComplexGeoData::getCenterOfGravity(Base::Vector3d& unused) const
     return false;
 }
 
+std::optional<Base::Vector3d> ComplexGeoData::centerOfGravity() const
+{
+    Base::Vector3d centerOfGravity;
+
+    if (getCenterOfGravity(centerOfGravity)) {
+        return centerOfGravity;
+    }
+
+    return {};
+}
+
 const std::string& ComplexGeoData::elementMapPrefix()
 {
     static std::string prefix(ELEMENT_MAP_PREFIX);

src/App/ComplexGeoData.h

@@ -28,6 +28,8 @@
 #define APP_COMPLEX_GEO_DATA_H
 
 #include <algorithm>
+#include <optional>
+
 #include <Base/Handle.h>
 #include <Base/Matrix.h>
 #include <Base/Persistence.h>
@@ -200,6 +202,7 @@ public:
      * The default implementation only returns false.
      */
     virtual bool getCenterOfGravity(Base::Vector3d& center) const;
+    virtual std::optional<Base::Vector3d> centerOfGravity() const;
     //@}
 
     static const std::string& elementMapPrefix();