Optimize helper event listeners.

Most of the core helpers don't use event listeners. Stubbing out the
methods saves 6 calls to method_exists() per helper.

src/View/Helper/FormHelper.php

@@ -2171,4 +2171,13 @@ class FormHelper extends Helper {
 		return $this->_registry->get($name)->render($data);
 	}
 
+/**
+ * Event listeners.
+ *
+ * @return array
+ */
+	public function implementedEvents() {
+		return [];
+	}
+
 }

src/View/Helper/HtmlHelper.php

@@ -1237,4 +1237,13 @@ class HtmlHelper extends Helper {
 		return $configs;
 	}
 
+/**
+ * Event listeners.
+ *
+ * @return array
+ */
+	public function implementedEvents() {
+		return [];
+	}
+
 }

src/View/Helper/NumberHelper.php

@@ -218,4 +218,13 @@ class NumberHelper extends Helper {
 		return $this->_engine->defaultCurrency($currency);
 	}
 
+/**
+ * Event listeners.
+ *
+ * @return array
+ */
+	public function implementedEvents() {
+		return [];
+	}
+
 }

src/View/Helper/PaginatorHelper.php

@@ -808,4 +808,13 @@ class PaginatorHelper extends Helper {
 		return $out;
 	}
 
+/**
+ * Event listeners.
+ *
+ * @return array
+ */
+	public function implementedEvents() {
+		return ['View.beforeRender' => 'beforeRender'];
+	}
+
 }

src/View/Helper/RssHelper.php

@@ -351,4 +351,13 @@ class RssHelper extends Helper {
 		return $xml;
 	}
 
+/**
+ * Event listeners.
+ *
+ * @return array
+ */
+	public function implementedEvents() {
+		return [];
+	}
+
 }

src/View/Helper/SessionHelper.php

@@ -158,4 +158,13 @@ class SessionHelper extends Helper {
 		return Session::valid();
 	}
 
+/**
+ * Event listeners.
+ *
+ * @return array
+ */
+	public function implementedEvents() {
+		return [];
+	}
+
 }

src/View/Helper/TextHelper.php

@@ -325,4 +325,13 @@ class TextHelper extends Helper {
 		return $this->_engine->toList($list, $and, $separator);
 	}
 
+/**
+ * Event listeners.
+ *
+ * @return array
+ */
+	public function implementedEvents() {
+		return [];
+	}
+
 }

src/View/Helper/TimeHelper.php

@@ -446,4 +446,13 @@ class TimeHelper extends Helper {
 		return $this->_engine->i18nFormat($date, $format, $invalid, $timezone);
 	}
 
+/**
+ * Event listeners.
+ *
+ * @return array
+ */
+	public function implementedEvents() {
+		return [];
+	}
+
 }