LibWeb: Move use pseudo element styles from TreeBuilder to StyleComputer

The styling of elements using the `use_pseudo_element()` was only
applied on layout. When an element style was recomputed later that
styling was not overruled with the pseudo element selector styles.
This moves the styling override from `TreeBuilder.cpp` to
`StyleComputer.cpp`. Now the styles are always correctly applied.
I also removed the method `property_id_by_index()` because it was
not needed anymore.

Als some calls to `invalidate_layout()` in the Meter, Progress and
Select elements where not needed anymore because the style values
are update on the changing of the style attribute.

This fixes issue #22278.

Tests/LibWeb/Layout/input/element-use-pseudo-element.html

@@ -0,0 +1,9 @@
+<style>
+    * {
+        font: 20px 'SerenitySans';
+    }
+</style>
+<progress id="a"></progress>
+<script>
+    a.style.backgroundColor = 'red'; // Trigger style invalidation
+</script>