MDL-65292 style: Fix all function declarations white space

This has been generated running the following Sniffs, all
them part of the Moodle's CodeSniffer standard:
- PSR12.Functions.ReturnTypeDeclaration
- PSR12.Functions.NullableTypeDeclaration
- moodle.Methods.MethodDeclarationSpacing
- Squiz.Whitespace.ScopeKeywordSpacing

All them are, exclusively, about correct spacing, so the changes
are, all them, only white space changes.

Only exceptions to the above are 3 changes what were setting the
return type in a new line, and, when that happens, the closing
parenthesis (bracket) has to go to the same line than the colon.

message/output/email/classes/task/send_email_task.php

@@ -108,7 +108,7 @@ class send_email_task extends scheduled_task {
      *
      * @return moodle_recordset A moodle_recordset instance.
      */
-    private function get_unique_users() : moodle_recordset {
+    private function get_unique_users(): moodle_recordset {
         global $DB;
 
         $subsql = 'SELECT DISTINCT(useridto) as id
@@ -128,7 +128,7 @@ class send_email_task extends scheduled_task {
      * @param int $userid The ID of the user we are sending a digest to.
      * @return moodle_recordset A moodle_recordset instance.
      */
-    private function get_conversations_for_user(int $userid) : moodle_recordset {
+    private function get_conversations_for_user(int $userid): moodle_recordset {
         global $DB;
 
         // We shouldn't be joining directly on the group table as group
@@ -158,7 +158,7 @@ class send_email_task extends scheduled_task {
      * @param int $userid
      * @return moodle_recordset A moodle_recordset instance.
      */
-    protected function get_users_messages_for_conversation(int $conversationid, int $userid) : moodle_recordset {
+    protected function get_users_messages_for_conversation(int $conversationid, int $userid): moodle_recordset {
         global $DB;
 
         $userfieldsapi = \core_user\fields::for_userpic();