MDL-83109 theme: Update core:t/completion_fail icon and resize it

This commit:
- Updates core:t/completion_fail from fa-times to fa-xmark
- Reduces the font size of course index completion icons from 12px to 10px.

lib/classes/output/icon_system_fontawesome.php

@@ -388,7 +388,7 @@ public function get_core_icon_map() {
             'core:t/collapsedchevron_rtl' => 'fa-chevron-left',
             'core:t/collapsedchevron_up' => 'fa-chevron-up',
             'core:t/completion_complete' => 'fa-circle',
-            'core:t/completion_fail' => 'fa-times',
+            'core:t/completion_fail' => 'fa-xmark',
             'core:t/completion_incomplete' => 'fa-regular fa-circle',
             'core:t/contextmenu' => 'fa-ellipsis-vertical',
             'core:t/copy' => 'fa-solid fa-clone',

theme/boost/scss/moodle/courseindex.scss

@@ -185,7 +185,7 @@ $courseindex-item-current: $primary !default;
 
     // General icons size.
     .icon {
-        font-size: 12px;
+        font-size: 10px;
     }
 
     // Element visible only on editing mode.

theme/boost/style/moodle.css

@@ -38749,7 +38749,7 @@ div.editor_atto_toolbar button .icon {
   width: 100%;
 }
 .courseindex .icon {
-  font-size: 12px;
+  font-size: 10px;
 }
 .courseindex .d-flex-noedit {
   display: none;

theme/classic/style/moodle.css

@@ -38683,7 +38683,7 @@ div.editor_atto_toolbar button .icon {
   width: 100%;
 }
 .courseindex .icon {
-  font-size: 12px;
+  font-size: 10px;
 }
 .courseindex .d-flex-noedit {
   display: none;