Rename _animation.scss to _transitions.scss

Fixes #21327 (closed).

docs/components/collapse.md

@@ -104,7 +104,7 @@ The collapse plugin utilizes a few classes to handle the heavy lifting:
 - `.collapse.active` shows the content
 - `.collapsing` is added when the transition starts, and removed when it finishes
 
-These classes can be found in `_animation.scss`.
+These classes can be found in `_transitions.scss`.
 
 ### Via data attributes
 

scss/_transitions.scss

 .fade {
   opacity: 0;
-
   @include transition($transition-fade);
 
   &.active {
@@ -31,6 +30,5 @@ tbody {
   position: relative;
   height: 0;
   overflow: hidden;
-
   @include transition($transition-collapse);
 }

scss/bootstrap.scss

@@ -25,7 +25,7 @@
 @import "buttons";
 
 // Components
-@import "animation";
+@import "transitions";
 @import "dropdown";
 @import "button-group";
 @import "input-group";