Merge pull request w3c#6654 from litherum/palette-properties-mutable

[css-fonts] [palettes] Properties in CSSFontPaletteValuesRule don't need to be mutable

Author: svgeesus

css-fonts-4/Overview.bs

@@ -6878,10 +6878,11 @@ a single value.
 The <code id="cssfontpalettevaluesrule2">CSSFontPaletteValuesRule</code> interface</h3>
 <pre class='idl'>[Exposed=Window]
 interface CSSFontPaletteValuesRule : CSSRule {
-  attribute CSSOMString name;
-  attribute CSSOMString fontFamily;
-  attribute CSSOMString basePalette;
-  attribute CSSOMString overrideColor;
+  readonly attribute CSSOMString basePalette;
+  readonly attribute CSSOMString name;
+  readonly attribute CSSOMString fontFamily;
+  readonly attribute CSSOMString basePalette;
+  readonly attribute CSSOMString overrideColor;
 };</pre>
 
 The value of the 'maplike' function [=CSS/parses=] as a <<color>>. If it is not a color,