Change MH to use the module_utils.vardict.VarDict (#8226)

* change MH to use the module_utils.vardict.VarDict

* remove VarsMixin from superclasses of MH

* bump vardict deprecation to 11.0.0 + add old/new vardict selection in MH

* improve backawards compatibility

* improve backawards compatibility

* use new vardict in some modules, make adjustments

* add changelog frag

* adjustment after rebase

plugins/modules/opkg.py

@@ -127,6 +127,7 @@ class Opkg(StateModuleHelper):
             executable=dict(type="path"),
         ),
     )
+    use_old_vardict = False
 
     def __init_module__(self):
         self.vars.set("install_c", 0, output=False, change=True)