add isReducedMotion util (#333)

src/lang/util.ts

@@ -26,3 +26,12 @@ export function updateCursors(
     setCursor(newSelections)
   }
 }
+
+export function isReducedMotion(): boolean {
+  return (
+    typeof window !== 'undefined' &&
+    window.matchMedia &&
+    // TODO/Note I (Kurt) think '(prefers-reduced-motion: reduce)' and '(prefers-reduced-motion)' are equivalent, but not 100% sure
+    window.matchMedia('(prefers-reduced-motion)').matches
+  )
+}