Add a generic parameter <E> to getExternalInstance (#986)

* Add a generic parameter <E> to getExternalInstance

To avoid getting warning: [unchecked] unchecked cast when generated code uses this method.
So now instead of being declared as

public ArrayList getExternalInstance()

it is declared as

public <E> ArrayList<E> getExternalInstance()

with <E> being the type parameter.
You can then call the method passing an explicit parameter, e.g.:

chatHistory.<OpenAIResponse.Message>getExternalInstance();

which we currently don't generate, but just using

chatHistory.getExternalInstance();

also does not yield a warning.

* Add generics ni array creation and cast in add method

---------

Co-authored-by: Gustavo Brown Rodriguez <gustavo.brown@globant.com>
Co-authored-by: iroqueta <iroqueta@genexus.com>

Author: 3 people

common/src/main/java/com/genexus/GXExternalCollection.java

@@ -100,13 +100,13 @@ public Vector getStruct()
 	}
 
 	@SuppressWarnings("unchecked")
-	public ArrayList getExternalInstance() {
-		ArrayList list = new ArrayList();
+	public <E> ArrayList<E> getExternalInstance() {
+		ArrayList<E> list = new ArrayList<>();
 		for (T Item : this)
 		{
 			try
 			{
-				list.add(Item.getClass().getMethod("getExternalInstance", new Class[]{}).invoke(Item));
+				list.add((E) Item.getClass().getMethod("getExternalInstance", new Class[]{}).invoke(Item));
 			}
 			catch (Exception e)
 			{