Auto merge of #18069 - hiikezoe:scroll-snap, r=daisuke

Make scroll-snap-{coordinate, destination} discrete animation.

<!-- Please describe your changes on the following line: -->
https://bugzilla.mozilla.org/show_bug.cgi?id=1387941

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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components/style/properties/longhand/box.mako.rs

@@ -721,7 +721,7 @@ ${helpers.predefined_type("scroll-snap-destination",
                           products="gecko",
                           boxed="True",
                           spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-destination)",
-                          animation_value_type="ComputedValue")}
+                          animation_value_type="discrete")}
 
 ${helpers.predefined_type(
     "scroll-snap-coordinate",
@@ -730,7 +730,7 @@ ${helpers.predefined_type(
     vector=True,
     products="gecko",
     spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-destination)",
-    animation_value_type="ComputedValue",
+    animation_value_type="discrete",
     allow_empty="NotInitial"
 )}