Joomla Dialog use svg loader (joomla#45097)

Thank you to all who worked on this and to the testers who put the work into testing
@Fedik, can you take a look at Brian's comment
Does this resolve the open issues joomla#31078 and joomla#30099

Author: Fedik

build/media_source/system/images/joomla-loader.svg

@@ -220,7 +220,8 @@ joomla-dialog {
         width: 66px;
         height: 66px;
         content: "";
-        background: url("../../../../system/images/ajax-loader.gif") no-repeat center; // TODO: use svg animation?
+        background: url("../../../../system/images/joomla-loader.svg") no-repeat center;
+        background-size: 66px 66px;
         transform: translate(-50%, -50%);
       }
     }

build/media_source/templates/administrator/atum/scss/blocks/_modals.scss

@@ -85,7 +85,8 @@ joomla-dialog {
         width: 66px;
         height: 66px;
         content: "";
-        background: url("../../../../system/images/ajax-loader.gif") no-repeat center;
+        background: url("../../../../system/images/joomla-loader.svg") no-repeat center;
+        background-size: 66px 66px;
         transform: translate(-50%, -50%);
       }
     }