fix: 3 char hex color is incorrectly modified to 6 (#4013)

The current logic creates `cdecde` from `cde`, it should be `ccddee`.

@dsevillamartin said this is the code to use instead and chat gpt said he's brilliant so..

framework/core/js/src/common/utils/isDark.ts

@@ -17,7 +17,7 @@ export default function isDark(hexcolor: string | null): boolean {
   let hexnumbers = hexcolor.replace('#', '');
 
   if (hexnumbers.length === 3) {
-    hexnumbers += hexnumbers;
+    hexnumbers = hexnumbers.split('').map(char => char.repeat(2)).join('');
   }
 
   const r = parseInt(hexnumbers.slice(0, 2), 16);