MDL-53695 minify: switch to MatthiasMullie\Minify

The previously used minification libraries were:
a) Unmaintained
b) Had some silly licensing issues (MDL-36457)

The new library is smaller, maintained, active and GPL-compatible.

lib/classes/component.php

@@ -79,7 +79,9 @@ class core_component {
         'Sabberworm\\CSS' => 'lib/php-css-parser',
         'MoodleHQ\\RTLCSS' => 'lib/rtlcss',
         'Leafo\\ScssPhp' => 'lib/scssphp',
-        'Box\\Spout' => 'lib/spout/src/Spout'
+        'Box\\Spout' => 'lib/spout/src/Spout',
+        'MatthiasMullie\\Minify' => 'lib/minify/matthiasmullie-minify/src/',
+        'MatthiasMullie\\PathConverter' => 'lib/minify/matthiasmullie-pathconverter/src/',
     );
 
     /**