Allow actors to override the entity's anchor type

Optionally let actor templates define their own anchor types.
These override the default value defined in the template.
Useful for actors without their own entity template.

Reviewed-By: Itms
Reviewed-On: https://gitea.wildfiregames.com/0ad/0ad/pulls/7542

source/graphics/ObjectBase.cpp

@@ -60,6 +60,7 @@ CObjectBase::CObjectBase(CObjectManager& objectManager, CActorDef& actorDef, u8
 : m_ObjectManager(objectManager), m_ActorDef(actorDef)
 {
 	m_QualityLevel = qualityLevel;
+	m_Properties.m_AnchorType = "";
 	m_Properties.m_CastShadows = false;
 	m_Properties.m_FloatOnWater = false;
 
@@ -82,6 +83,7 @@ bool CObjectBase::Load(const CXeromyces& XeroFile, const XMBElement& root)
 	// Define all the elements used in the XML file
 #define EL(x) int el_##x = XeroFile.GetElementID(#x)
 #define AT(x) int at_##x = XeroFile.GetAttributeID(#x)
+	EL(anchor);
 	EL(castshadow);
 	EL(float);
 	EL(group);
@@ -143,6 +145,8 @@ bool CObjectBase::Load(const CXeromyces& XeroFile, const XMBElement& root)
 				return false;
 			}
 		}
+		else if (child_name == el_anchor)
+			m_Properties.m_AnchorType = child.GetText();
 		else if (child_name == el_castshadow)
 			m_Properties.m_CastShadows = true;
 		else if (child_name == el_float)