Moved all required styling for Editor

Instead of relying on specific utility classes being present in
HTML, we move the styling into CSS to make sure we have
everything that we need for the dimensions and positioning of
the editor

Also introduced the default values for the spinner mixin

app/assets/stylesheets/framework/editor-lite.scss

-[data-editor-loading]::before {
+[data-editor-loading] {
+  @include gl-relative;
+  @include gl-display-flex;
+  @include gl-justify-content-center;
+  @include gl-align-items-center;
+
+  &::before {
     content: '';
-  @include spinner(32px, 3px, $orange-400);
+    @include spinner(32px, 3px);
     @include gl-absolute;
     @include gl-z-index-1;
+  }
+
+  pre {
+    opacity: 0;
+  }
 }
 
 [id^='editor-lite-'] {

app/assets/stylesheets/framework/spinner.scss

@@ -20,7 +20,7 @@
   }
 }
 
-@mixin spinner($size, $border-width, $color) {
+@mixin spinner($size: 16px, $border-width: 2px, $color: $orange-400) {
   border-radius: 50%;
   position: relative;
   margin: 0 auto;
@@ -35,7 +35,7 @@
 }
 
 .spinner {
-  @include spinner(16px, 2px, $orange-400);
+  @include spinner;
 
   &.spinner-md {
     @include spinner-size(32px, 3px);