Migrate loading icon to be Pajamas compliant

Migrated the current loading icon to the new `gl-loading-icon`

app/assets/javascripts/blob/template_selector.js

@@ -2,6 +2,7 @@
 
 import $ from 'jquery';
 import initDeprecatedJQueryDropdown from '~/deprecated_jquery_dropdown';
+import { loadingIconForLegacyJS } from '~/loading_icon_for_legacy_js';
 
 export default class TemplateSelector {
   constructor({ dropdown, data, pattern, wrapper, editor, $input } = {}) {
@@ -10,10 +11,9 @@ export default class TemplateSelector {
     this.dropdown = dropdown;
     this.$dropdownContainer = wrapper;
     this.$filenameInput = $input || $('#file_name');
-    this.$dropdownIcon = $('.dropdown-menu-toggle-icon', dropdown);
-    this.$loadingIcon = $(
-      '<div class="gl-spinner gl-spinner-orange gl-spinner-sm gl-absolute gl-top-3 gl-right-3 gl-display-none"></div>',
-    ).insertAfter(this.$dropdownIcon);
+    this.dropdownIcon = dropdown[0].querySelector('.dropdown-menu-toggle-icon');
+    this.loadingIcon = loadingIconForLegacyJS({ classes: ['gl-display-none'] });
+    this.dropdownIcon.parentNode.insertBefore(this.loadingIcon, this.dropdownIcon.nextSibling);
 
     this.initDropdown(dropdown, data);
     this.listenForFilenameInput();
@@ -100,12 +100,12 @@ export default class TemplateSelector {
   }
 
   startLoadingSpinner() {
-    this.$loadingIcon.removeClass('gl-display-none');
-    this.$dropdownIcon.addClass('gl-display-none');
+    this.loadingIcon.classList.remove('gl-display-none');
+    this.dropdownIcon.classList.add('gl-display-none');
   }
 
   stopLoadingSpinner() {
-    this.$loadingIcon.addClass('gl-display-none');
-    this.$dropdownIcon.removeClass('gl-display-none');
+    this.loadingIcon.classList.add('gl-display-none');
+    this.dropdownIcon.classList.remove('gl-display-none');
   }
 }

app/assets/javascripts/issues/show/components/fields/description_template.vue

@@ -68,7 +68,10 @@ export default {
       data-toggle="dropdown"
     >
       <span class="dropdown-toggle-text">{{ __('Choose a template') }}</span>
-      <gl-icon name="chevron-down" class="gl-absolute gl-top-3 gl-right-3 gl-text-gray-500" />
+      <gl-icon
+        name="chevron-down"
+        class="gl-absolute gl-top-3 gl-right-3 gl-text-gray-500 dropdown-menu-toggle-icon"
+      />
     </button>
     <div class="dropdown-menu dropdown-select">
       <div class="dropdown-title gl-display-flex gl-justify-content-center">