Rename animatable to animation_type.

animation_type takes following values:

animation_type="none" for non-animatable properties
animation_type="normal" for animatable properties
animation_type="discrete" for animatable but discrete type of animations

We use string value to distinguish the case where no animation_type is
specified.
animation_type="discrete" will be used in a subsequent patch to make a property
animatable as discrete type.

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

@@ -7,12 +7,12 @@
 <% data.new_style_struct("Table", inherited=False) %>
 
 ${helpers.single_keyword("table-layout", "auto fixed",
-                         gecko_ffi_name="mLayoutStrategy", animatable=False,
+                         gecko_ffi_name="mLayoutStrategy", animation_type="none",
                          spec="https://drafts.csswg.org/css-tables/#propdef-table-layout")}
 
 <%helpers:longhand name="-x-span" products="gecko"
                    spec="Internal-only (for `<col span>` pres attr)"
-                   animatable="False"
+                   animation_type="none"
                    internal="True">
     use values::HasViewportPercentage;
     use values::computed::ComputedValueAsSpecified;