Refactor dependency on widget.getVariableInfo

Fixing https://talk.tiddlywiki.org/t/tw-v5-3-0-pre-problem-with-autocomplete-plugin/6958/9?u=jeremyruston

core/modules/filters.js

@@ -12,6 +12,8 @@ Adds tiddler filtering methods to the $tw.Wiki object.
 /*global $tw: false */
 "use strict";
 
+var widgetClass = require("$:/core/modules/widgets/widget.js").widget;
+
 /* Maximum permitted filter recursion depth */
 var MAX_FILTER_DEPTH = 300;
 
@@ -269,8 +271,7 @@ exports.compileFilter = function(filterString) {
 						operand.value = self.getTextReference(operand.text,"",currTiddlerTitle);
 					} else if(operand.variable) {
 						var varTree = $tw.utils.parseFilterVariable(operand.text);
-						var variableInfo = widget.getVariableInfo(varTree.name,{params: varTree.params, source: source});
-						operand.value = (variableInfo.resultList ? variableInfo.resultList[0] : variableInfo.text) || "";
+						operand.value = widgetClass.evaluateVariable(widget,varTree.name,{params: varTree.params, source: source})[0] || "";
 					} else {
 						operand.value = operand.text;
 					}

core/modules/widgets/widget.js

@@ -796,6 +796,20 @@ Widget.prototype.allowActionPropagation = function() {
 	return true;
 };
 
+/*
+Evaluate a variable with parameters. This is a static convenience method that attempts to evaluate a variable as a function, returning an array of strings
+*/
+Widget.evaluateVariable  = function(widget,name,options) {
+	var result;
+	if(widget.getVariableInfo) {
+		var variableInfo = widget.getVariableInfo(name,options);
+		result = variableInfo.resultList || [variableInfo.text];
+	} else {
+		result = [widget.getVariable(name)];
+	}
+	return result;
+};
+
 exports.widget = Widget;
 
 })();