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.

grade/renderer.php

@@ -158,7 +158,7 @@ class core_grades_renderer extends plugin_renderer_base {
      * @param bool $showbuttons Whether to display buttons (message, add to contacts) within the heading.
      * @return string The raw HTML to render.
      */
-    public function user_heading(stdClass $user, int $courseid, bool $showbuttons = true) : string {
+    public function user_heading(stdClass $user, int $courseid, bool $showbuttons = true): string {
         global $USER;
 
         $headingdata = [