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.

lib/classes/useragent.php

@@ -1183,7 +1183,7 @@ class core_useragent {
      * @param string $extension
      * @return bool
      */
-    public static function supports_media_source_extensions(string $extension) : bool {
+    public static function supports_media_source_extensions(string $extension): bool {
         // Not supported in IE below 11.0.
         if (self::is_ie() && !self::check_ie_version('11.0')) {
             return false;