Custom widgets and filter operator names must now contain a period

Fixes #7428

editions/test/tiddlers/tests/data/transclude/CustomWidget-ActionWidget.tid

@@ -12,15 +12,15 @@ title: Output
 title: Actions
 
 \whitespace trim
-<!-- Define the <$$action-mywidget> widget by defining a transcludable variable with that name -->
-\widget $$action-mywidget(one:'Jaguar')
+<!-- Define the <$action.mywidget> widget by defining a transcludable variable with that name -->
+\widget $action.mywidget(one:'Jaguar')
 \whitespace trim
 <$action-setfield $tiddler="Result" $field="text" $value=<<one>>/>
 \end
 
-<$$action-mywidget one="Dingo">
+<$action.mywidget one="Dingo">
 	Crocodile
-</$$action-mywidget>
+</$action.mywidget>
 +
 title: ExpectedResult