[Glitch] Use LoadingBar instead of blur to indicate that an image is loading

Port 955d5d36e8 to the glitch-soc flavour

app/javascript/flavours/glitch/styles/components/index.scss

@@ -339,6 +339,7 @@
   display: flex;
   align-items: center;
   justify-content: center;
+  flex-direction: column;
 
   .image-loader__preview-canvas {
     max-width: $media-modal-media-max-width;
@@ -347,8 +348,8 @@
     object-fit: contain;
   }
 
-  &.image-loader--loading .image-loader__preview-canvas {
-    filter: blur(2px);
+  .loading-bar {
+    position: relative;
   }
 
   &.image-loader--amorphous .image-loader__preview-canvas {