Add has_action method

Changelog.md

@@ -14,6 +14,7 @@
      - An identicon is rendered if a user hasn't specified an email address or uploaded a gravatar yet either
      - Added `avatars_show` and `avatars_size` settings to control the displaying & size of rendered avatars.
      - Added the `avatar` action, which 307 redirects to the appropriate avatar image
+ - Added `has_action` to make detecting enabled features easier (even if they move modules)
 
 ### Changed
  - Updated MathJax CDN link, as cdn.mathjax.org is being retired ([source](https://www.mathjax.org/cdn-shutting-down/)).

build/index.php

@@ -1720,6 +1720,17 @@ function add_action($action_name, $func)
 	global $actions;
 	$actions->$action_name = $func;
 }
+/**
+ * Figures out whether a given action is currently registered.
+ * Only guaranteed to be accurate in inside an existing action function
+ * @param  string  $action_name The name of the action to search for
+ * @return boolean              Whether an action with the specified name exists.
+ */
+function has_action($action_name)
+{
+	global $actions;
+	return !empty($actions->action_name);
+}
 
 $parsers = [
 	"none" => function() {

core.php

@@ -1371,6 +1371,17 @@ function add_action($action_name, $func)
 	global $actions;
 	$actions->$action_name = $func;
 }
+/**
+ * Figures out whether a given action is currently registered.
+ * Only guaranteed to be accurate in inside an existing action function
+ * @param  string  $action_name The name of the action to search for
+ * @return boolean              Whether an action with the specified name exists.
+ */
+function has_action($action_name)
+{
+	global $actions;
+	return !empty($actions->action_name);
+}
 
 $parsers = [
 	"none" => function() {