move get collection recursive in functions so it can be reused

fn.py

@@ -307,6 +307,18 @@ def connect_to_file_output(node_list, file_out=None, base_path='', excludes=None
 
 # region Utilities
 
+def get_collection_children_recursive(col, cols=None) -> list:
+    '''return a list of all the child collections
+    and their subcollections in the passed collection'''
+
+    cols = cols if cols is not None else []
+    for sub in col.children:
+        if sub not in cols:
+            cols.append(sub)
+        if len(sub.children):
+            cols = get_collection_children_recursive(sub, cols)
+    return cols
+
 def set_properties_editor_tab(tab, skip_if_exists=True):
     '''Take a tab name and apply it to properties editor
     tab: identifier of the tab, possible name in: