Return CSSStyleProperties from element.style and getComputedStyle

Followup for #9686

Author: saschanaz

cssom-1/Overview.bs

@@ -3052,11 +3052,11 @@ The <code>ElementCSSInlineStyle</code> mixin provides access to inline style pro
 
 <pre class=idl>
 interface mixin ElementCSSInlineStyle {
-  [SameObject, PutForwards=cssText] readonly attribute CSSStyleDeclaration style;
+  [SameObject, PutForwards=cssText] readonly attribute CSSStyleProperties style;
 };
 </pre>
 
-The <dfn attribute for=ElementCSSInlineStyle>style</dfn> attribute must return a <a>CSS declaration block</a> object whose
+The <dfn attribute for=ElementCSSInlineStyle>style</dfn> attribute must return a <a>CSSStyleProperties</a> object whose
 <a for="CSSStyleDeclaration">readonly flag</a> is unset, whose <a for="CSSStyleDeclaration">parent CSS rule</a> is null, and
 whose <a for="CSSStyleDeclaration">owner node</a> is [=this=].
 
@@ -3083,7 +3083,7 @@ Extensions to the {{Window}} Interface {#extensions-to-the-window-interface}
 
 <pre class=idl>
 partial interface Window {
-  [NewObject] CSSStyleDeclaration getComputedStyle(Element elt, optional CSSOMString? pseudoElt);
+  [NewObject] CSSStyleProperties getComputedStyle(Element elt, optional CSSOMString? pseudoElt);
 };
 </pre>