style: Make text-orientation, unicode-bidi, contain and will-change non-animatable.

Per recent CSSWG resolutions:

  https://github.com/w3c/csswg-drafts/issues/2737
  https://github.com/w3c/csswg-drafts/issues/2751

Differential Revision: https://phabricator.services.mozilla.com/D3888

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

@@ -40,15 +40,12 @@ ${helpers.single_keyword(
     servo_restyle_damage="rebuild_and_reflow",
 )}
 
-// TODO(emilio): Should text-orientation be non-animatable? It affects the
-// WritingMode value, but not the logical -> physical mapping of properties,
-// which is the reason direction / writing-mode are non-animatable.
 ${helpers.single_keyword(
     "text-orientation",
     "mixed upright sideways",
     extra_gecko_aliases="sideways-right=sideways",
     products="gecko",
-    animation_value_type="discrete",
+    animation_value_type="none",
     spec="https://drafts.csswg.org/css-writing-modes/#propdef-text-orientation",
 )}