style: Parse scroll-snap-stop style and propagate it to APZ side

Depends on D146147

Differential Revision: https://phabricator.services.mozilla.com/D145850

components/style/properties/counted_unknown_properties.py

@@ -73,7 +73,6 @@ COUNTED_UNKNOWN_PROPERTIES = [
     "-webkit-perspective-origin-y",
     "-webkit-margin-before-collapse",
     "-webkit-border-before-style",
-    "scroll-snap-stop",
     "-webkit-margin-bottom-collapse",
     "-webkit-ruby-position",
     "-webkit-column-break-after",

components/style/properties/data.py

@@ -492,6 +492,7 @@ class Longhand(Property):
                 "ScrollbarGutter",
                 "ScrollSnapAlign",
                 "ScrollSnapAxis",
+                "ScrollSnapStop",
                 "ScrollSnapStrictness",
                 "ScrollSnapType",
                 "TextAlign",

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

@@ -285,6 +285,15 @@ ${helpers.predefined_type(
     animation_value_type="discrete",
 )}
 
+${helpers.predefined_type(
+    "scroll-snap-stop",
+    "ScrollSnapStop",
+    "computed::ScrollSnapStop::Normal",
+    engines="gecko",
+    spec="https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-stop",
+    animation_value_type="discrete",
+)}
+
 % for (axis, logical) in ALL_AXES:
     ${helpers.predefined_type(
         "overscroll-behavior-" + axis,