Add image-animation-1.vim

https://www.w3.org/TR/2026/WD-css-image-animation-1-20260409/

after/syntax/css/image-animation-1.vim

@@ -0,0 +1,3 @@
+syn keyword cssFontProp contained image-animation
+syn keyword cssFontAttr contained stopped
+syn keyword cssPseudoClassId contained animated-image

test/test.css

@@ -683,6 +683,11 @@ template {
   display: auto;
 }
 
+.image-animation-1:animated-image {
+  image-animation: auto;
+  display: stopped;
+}
+
 .images-3 {
   image-orientation: auto;
   display: snap;