Formatter: Added PSAvoidTrailingWhitespace to the list of rules considered by the formatter

Author: liamjpeters

Engine/Formatter.cs

@@ -47,6 +47,7 @@ public static string Format<TCmdlet>(
                 "PSAvoidUsingDoubleQuotesForConstantString",
                 "PSAvoidSemicolonsAsLineTerminators",
                 "PSAvoidExclaimOperator",
+                "PSAvoidTrailingWhitespace",
             };
 
             var text = new EditableText(scriptDefinition);