LibWeb: Handle steps(x, start) like steps(x, jump-start)

Author: https://github.com/Gingeh
Commit: cd5d8f4d95
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2173
Reviewed-by: https://github.com/AtkinsSJ ✅

Tests/LibWeb/Text/input/WebAnimations/misc/easing-values.html

@@ -21,14 +21,14 @@
             "cubic-bezier(0, 0, 0, 0)",
             "cubic-bezier(1, 1, 1, 1)",
             "cubic-bezier(1, 1000, 1, 1000)",
-            // FIXME: "step-start",
+            "step-start",
             "step-end",
             "steps(1000)",
             "steps(10, jump-start)",
             "steps(10, jump-end)",
             "steps(10, jump-none)",
             "steps(10, jump-both)",
-            // FIXME: "steps(10, start)",
+            "steps(10, start)",
             "steps(10, end)",
         ];