LibWeb: Expose AnimationTimeline::currentTime as CSSNumberish

This also allows us to remove the now redundant
`CSSNumberishTime::as_milliseconds()` method

Author: Calme1709

Libraries/LibWeb/Animations/AnimationTimeline.h

@@ -17,9 +17,9 @@ class AnimationTimeline : public Bindings::PlatformObject {
     GC_DECLARE_ALLOCATOR(AnimationTimeline);
 
 public:
-    Optional<double> current_time_for_bindings() const
+    NullableCSSNumberish current_time_for_bindings() const
     {
-        return current_time().map([](auto const& current_time) { return current_time.as_milliseconds(); });
+        return NullableCSSNumberish::from_optional_css_numberish_time(current_time());
     }
     Optional<TimeValue> current_time() const;
 

Libraries/LibWeb/Animations/AnimationTimeline.idl

@@ -3,7 +3,7 @@
 // https://drafts.csswg.org/web-animations-2/#the-animationtimeline-interface
 [Exposed=Window]
 interface AnimationTimeline {
-    [ImplementedAs=current_time_for_bindings] readonly attribute double? currentTime;
+    [ImplementedAs=current_time_for_bindings] readonly attribute CSSNumberish? currentTime;
     [ImplementedAs=duration_for_bindings] readonly attribute CSSNumberish? duration;
     [FIXME] Animation play (optional AnimationEffect? effect = null);
 };

Libraries/LibWeb/Animations/TimeValue.h

@@ -77,13 +77,6 @@ struct TimeValue {
         return type == other.type && value == other.value;
     }
 
-    // FIXME: This method is temporary as we migrate all CSS timing to use TimeValue.
-    double as_milliseconds() const
-    {
-        VERIFY(type == Type::Milliseconds);
-        return value;
-    }
-
     CSS::CSSNumberish as_css_numberish() const
     {
         switch (type) {