web/core: Apply all properties to element in logical order

Previously, we would iterate the list of matched properties
in reverse order (most important first) and keep track of which
properties were set (using a hashset) to avoid less-important
values overriding more-important ones.

This wasn't perfect because shorthand properties set multiple
properties at once and its not trivial to keep track of that in
a nice way. Also we constantly need to allocate for the hashset
(no benchmarks, but it *sounds* slow)

Instead, we now iterate the list in logical order, applying
less-important rules first and then overriding them later if necessary.

crates/web/core/src/css/stylecomputer.rs

@@ -1,4 +1,4 @@
-use std::{cmp, collections::HashSet, mem};
+use std::cmp;
 
 use crate::{
     css::{
@@ -169,15 +169,11 @@ impl<'a> StyleComputer<'a> {
         matched_properties.sort_unstable_by(MatchingProperty::compare_in_cascade_order);
         let mut computed_style = parent_style.get_inherited();
 
-        // Add properties in reverse order (most important first)
-        let mut properties_added = HashSet::new();
-
-        for matched_property in matched_properties.into_iter().rev() {
+        // Add properties in logical order (least important first)
+        // That way, more important rules can override less important ones
+        for matched_property in matched_properties.into_iter() {
             let property = matched_property.into_property();
-
-            if properties_added.insert(mem::discriminant(&property)) {
-                computed_style.set_property(property);
-            }
+            computed_style.set_property(property);
         }
 
         computed_style