MDL-65292 style: Fix all the function declaration ordering

This has been generated running the following Sniff,
part of the Moodle's CodeSniffer standard:
- PSR2.Methods.MethodDeclaration

It just ensures all the function declarations have
the correct order for:
- abstract and final.
- visibility (public, protected, private).
- static.

So, all the lines modified by this commit are function declarations
and the only changes are in the positions of those keywords.

lib/classes/message/inbound/handler.php

@@ -204,7 +204,7 @@ abstract class handler {
      *
      * @return string
      */
-    protected abstract function get_description();
+    abstract protected function get_description();
 
     /**
      * Return a name for the current handler.
@@ -212,7 +212,7 @@ abstract class handler {
      *
      * @return string
      */
-    protected abstract function get_name();
+    abstract protected function get_name();
 
     /**
      * Process the message against the current handler.
@@ -220,7 +220,7 @@ abstract class handler {
      * @param \stdClass $record The Inbound Message Handler record
      * @param \stdClass $messagedata The message data
      */
-    public abstract function process_message(\stdClass $record, \stdClass $messagedata);
+    abstract public function process_message(\stdClass $record, \stdClass $messagedata);
 
     /**
      * Return the content of any success notification to be sent.