Expose StylePropertyMap.set on Window only. (w3c#597)

* Expose StylePropertyMap.set on Window only.

* Only expose StylePropertyMapReadOnly to PaintWorklet,Window

* typo

* Add [Exposed] to StylePropertyMap

Author: nainar

css-typed-om/Overview.bs

@@ -195,6 +195,7 @@ The {{StylePropertyMap}} {#the-stylepropertymap}
 ================================================
 
 <xmp class='idl'>
+[Exposed=Window,PaintWorklet]
 interface StylePropertyMapReadOnly {
     readonly maplike<DOMString, sequence<CSSStyleValue>>;
     any get(DOMString property);
@@ -207,6 +208,7 @@ interface StylePropertyMapReadOnly {
 
 callback UpdateFunction = CSSStyleValue (CSSStyleValue oldValue);
 
+[Exposed=Window]
 interface StylePropertyMap : StylePropertyMapReadOnly {
     maplike<DOMString, sequence<CSSStyleValue>>;
     void append(DOMString property, (CSSStyleValue or DOMString)... values);