Add setting for the formatter to trim trailing whitespace

Author: liamjpeters

src/PowerShellEditorServices/Services/Workspace/LanguageServerSettings.cs

@@ -208,6 +208,7 @@ public CodeFormattingSettings(CodeFormattingSettings codeFormattingSettings)
         public bool IgnoreOneLineBlock { get; set; }
         public bool AlignPropertyValuePairs { get; set; }
         public bool UseCorrectCasing { get; set; }
+        public bool RemoveTrailingWhitespace { get; set; }
 
         /// <summary>
         /// Get the settings hashtable that will be consumed by PSScriptAnalyzer.
@@ -328,6 +329,13 @@ private Hashtable GetCustomPSSASettingsHashtable(int tabSize, bool insertSpaces)
                 ruleConfigurations.Add("PSAvoidUsingCmdletAliases", new Hashtable());
             }
 
+            if (RemoveTrailingWhitespace)
+            {
+                // Empty hashtable required to activate the rule,
+                // since PSAvoidTrailingWhitespace inherits from IScriptRule and not ConfigurableRule
+                ruleConfigurations.Add("PSAvoidTrailingWhitespace", new Hashtable());
+            }
+
             return new Hashtable()
             {
                 { "IncludeRules", new string[] {