ModuleHelper - better mechanism for customizing "changed" behaviour (#2514) (#2546)

* better mechanism for customizing "changed" behaviour

* dont drink and code: silly mistake from late at night

* added changelog fragment

(cherry picked from commit 2a376642dd)

Co-authored-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>

changelogs/fragments/2514-mh-improved-changed.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - ModuleHelper module utils - improved mechanism for customizing the calculation of ``changed`` (https://github.com/ansible-collections/community.general/pull/2514).

plugins/module_utils/mh/base.py

@@ -33,9 +33,15 @@ class ModuleHelperBase(object):
     def __quit_module__(self):
         pass
 
+    def __changed__(self):
+        raise NotImplementedError()
+
     @property
     def changed(self):
-        return self._changed
+        try:
+            return self.__changed__()
+        except NotImplementedError:
+            return self._changed
 
     @changed.setter
     def changed(self, value):