style: Rename ScrollSnapType to ScrollSnapStrictness.

The scroll snap strictness is defined in the new spec [1], and the structure
is the exactly same as the old scroll snap type structure.

[1] https://drafts.csswg.org/css-scroll-snap-1/#snap-strictness

Differential Revision: https://phabricator.services.mozilla.com/D21621

components/style/properties/data.py

@@ -341,7 +341,7 @@ class Longhand(object):
                 "SVGOpacity",
                 "SVGPaintOrder",
                 "ScrollSnapAlign",
-                "ScrollSnapType",
+                "ScrollSnapStrictness",
                 "TextAlign",
                 "TextDecorationLine",
                 "TextEmphasisPosition",

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

@@ -430,8 +430,8 @@ ${helpers.predefined_type(
 % for axis in ["x", "y"]:
     ${helpers.predefined_type(
         "scroll-snap-type-" + axis,
-        "ScrollSnapType",
-        "computed::ScrollSnapType::None",
+        "ScrollSnapStrictness",
+        "computed::ScrollSnapStrictness::None",
         products="gecko",
         needs_context=False,
         gecko_pref="layout.css.scroll-snap.enabled",