[DURACOM-125][#8736] Preserved order of modified MetadataValues

feat:
  - Introduced new Class with static methods usable to order
`MetadataValue` lists;
  - Introduced ITs also for `PatchMetadata` replace operations;
  - Introduced new method `DspaceObject#getMetadataFieldId`.
ref:
  - Replaced old sort method inside `ItemServiceImpl` with the new one

dspace-api/src/main/java/org/dspace/content/MetadataValue.java

@@ -19,6 +19,7 @@ import javax.persistence.Lob;
 import javax.persistence.ManyToOne;
 import javax.persistence.SequenceGenerator;
 import javax.persistence.Table;
+import javax.persistence.Transient;
 
 import org.dspace.core.Context;
 import org.dspace.core.ReloadableEntity;
@@ -171,6 +172,14 @@ public class MetadataValue implements ReloadableEntity<Integer> {
         this.metadataField = metadataField;
     }
 
+    /**
+     * @return {@code MetadataField#getID()}
+     */
+    @Transient
+    protected Integer getMetadataFieldId() {
+        return getMetadataField().getID();
+    }
+
     /**
      * Get the metadata value.
      *