Mark WebP animation as supported in Edge 18 (#28769)

Author: ddbeck

mediatypes/image/webp.json

@@ -80,7 +80,9 @@
                 "version_added": "32"
               },
               "chrome_android": "mirror",
-              "edge": "mirror",
+              "edge": {
+                "version_added": "18"
+              },
               "firefox": {
                 "version_added": "65"
               },