Add macro operator (#9520)

* Add macro operator

* Replace unnecessary usage of wikify widget

* Simplify multiple let widget

* fixup! Replace unnecessary usage of wikify widget

* Update tests

* Update change note

* fixup! Replace unnecessary usage of wikify widget

* Update docs

* fixup! Update tests

core/modules/filters/macro.js

@@ -0,0 +1,27 @@
+/*\
+title: $:/core/modules/filters/macro.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator returning those input titles that are returned from a javascript macro
+
+\*/
+
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.macro = function(source,operator,options) {
+	const macroName = operator.operands[0],
+		results = [];
+	if($tw.macros[macroName] !== undefined) {
+		results.push($tw.macros[macroName].run(...operator.operands.slice(1)));
+	} else {
+		// Return the input list if the macro wasn't found
+		source((tiddler,title) => {
+			results.push(title);
+		});	
+	}
+	return results;
+};