style: Add -webkit-appearance:meter and make that the default for <me…

…ter> for compatibility with other UAs.

Keep our old value 'meterbar' as an alias for now, but unship 'meterchunk'
by restricting it to UA/chrome sheets only.

Bug: 1501483
Reviewed-by: jwatt

components/style/values/specified/box.rs

@@ -1036,8 +1036,10 @@ pub enum Appearance {
     #[parse(condition = "in_ua_or_chrome_sheet")]
     Menuimage,
     /// A horizontal meter bar.
-    Meterbar,
+    #[parse(aliases = "meterbar")]
+    Meter,
     /// The meter bar's meter indicator.
+    #[parse(condition = "in_ua_or_chrome_sheet")]
     Meterchunk,
     /// The "arrowed" part of the dropdown button that open up a dropdown list.
     #[parse(condition = "in_ua_or_chrome_sheet")]