style: Add unprefixed appearance property and make -moz-appearance and -webkit-appearance be aliases.

Differential Revision: https://phabricator.services.mozilla.com/D83428

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

@@ -615,22 +615,19 @@ ${helpers.predefined_type(
     spec="https://drafts.csswg.org/css-contain/#contain-property",
 )}
 
-// Non-standard
 ${helpers.predefined_type(
-    "-moz-appearance",
+    "appearance",
     "Appearance",
     "computed::Appearance::None",
     engines="gecko",
-    alias="-webkit-appearance",
-    spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-appearance)",
+    alias="-moz-appearance -webkit-appearance",
+    spec="https://drafts.csswg.org/css-ui-4/#propdef-appearance",
     animation_value_type="discrete",
     gecko_ffi_name="mAppearance",
 )}
 
-// A UA-sheet only property that is always set to the same value as
-// -moz-appearance.  Used to record telemetry for when author sheets
-// override the value of -moz-appearance; see
-// nsIFrame::RecordAppearanceTelemetry.
+// The inherent widget type of an element, selected by specifying
+// `appearance: auto`.
 ${helpers.predefined_type(
     "-moz-default-appearance",
     "Appearance",

components/style/style_adjuster.rs

@@ -763,10 +763,10 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
     where
         E: TElement,
     {
-        use crate::properties::longhands::_moz_appearance::computed_value::T as Appearance;
+        use crate::properties::longhands::appearance::computed_value::T as Appearance;
         use crate::properties::longhands::line_height::computed_value::T as LineHeight;
 
-        if self.style.get_box().clone__moz_appearance() == Appearance::Menulist {
+        if self.style.get_box().clone_appearance() == Appearance::Menulist {
             if self.style.get_inherited_text().clone_line_height() == LineHeight::normal() {
                 return;
             }

components/style/values/specified/box.rs

@@ -1525,6 +1525,11 @@ pub enum Resize {
 pub enum Appearance {
     /// No appearance at all.
     None,
+    /// Default appearance for the element.
+    ///
+    /// This value doesn't make sense for -moz-default-appearance, but we don't bother to guard
+    /// against parsing it.
+    Auto,
     /// A typical dialog button.
     Button,
     /// Various arrows that go in buttons