MDL-78983 core: Fix question mark icon direction flipping

This fixes the changes made in MDL-75047:
* Change `thisicondirection` langconfig string to a more specific one
  like `questionicondirection`.
* Use existing direction string value `ltr` for the value of
  `questionicondirection`. Also add a comment to at least provide some
  form of documentation for it.
* Improve the logic for applying the horizontal flipping class for the
  question icon:
  - Check first if the icon is a question icon
  - Flip the icon if `questionicondirection` is set to `rtl`.

lang/en/langconfig.php

@@ -41,6 +41,8 @@
 $string['parentlanguage'] = '';
 $string['pm'] = 'pm';
 $string['pmcaps'] = 'PM';
+// Direction of the question mark icon for this language. Set to 'rtl' if the language needs to display it in right-to-left.
+$string['questionicondirection'] = 'ltr';
 $string['strftimedate'] = '%d %B %Y';
 $string['strftimedatemonthabbr'] = '%d %b %Y';
 $string['strftimedatemonthtimeshort'] = '%d %b %Y, %I:%M';
@@ -64,7 +66,6 @@
 $string['strftimetime24'] = '%H:%M';
 $string['thisdirection'] = 'ltr';
 $string['thisdirectionvertical'] = 'btt';
-$string['thisicondirection'] = 'standard';
 $string['thislanguage'] = 'English';
 $string['thislanguageint'] = 'English';
 $string['thousandssep'] = ',';

lib/classes/output/icon_system_fontawesome.php

@@ -501,9 +501,8 @@ public function render_pix_icon(renderer_base $output, pix_icon $icon) {
             $data['aria-hidden'] = $icon->attributes['aria-hidden'];
         }
 
-        // Define the orientation of the question mark in right-to-left languages.
-        $mirror = get_string('thisicondirection', 'langconfig');
-        if ($mirror == 'mirror' && (strpos($data['key'], 'fa-question') !== false)) {
+        // Flip the orientation of the question mark if the value of the `questionicondirection` lang config string is set to `rtl`.
+        if (strpos($data['key'], 'fa-question') !== false && get_string('questionicondirection', 'langconfig') === 'rtl') {
             $data['extraclasses'] = "fa-flip-horizontal";
         }