Make spinners speed adjustable (#30154)

Author: GeoSot

scss/_spinners.scss

@@ -15,7 +15,7 @@
   border-right-color: transparent;
   // stylelint-disable-next-line property-blacklist
   border-radius: 50%;
-  animation: spinner-border .75s linear infinite;
+  animation: spinner-border $spinner-animation-speed linear infinite;
 }
 
 .spinner-border-sm {
@@ -46,7 +46,7 @@
   // stylelint-disable-next-line property-blacklist
   border-radius: 50%;
   opacity: 0;
-  animation: spinner-grow .75s linear infinite;
+  animation: spinner-grow $spinner-animation-speed linear infinite;
 }
 
 .spinner-grow-sm {

scss/_variables.scss

@@ -1208,9 +1208,10 @@ $carousel-transition:                transform $carousel-transition-duration eas
 
 // Spinners
 
-$spinner-width:         2rem !default;
-$spinner-height:        $spinner-width !default;
-$spinner-border-width:  .25em !default;
+$spinner-width:           2rem !default;
+$spinner-height:          $spinner-width !default;
+$spinner-border-width:    .25em !default;
+$spinner-animation-speed: .75s !default;
 
 $spinner-width-sm:        1rem !default;
 $spinner-height-sm:       $spinner-width-sm !default;