LibWeb: Handle interpolation of BorderRadius style value type

Author: https://github.com/MFMF-EGY 🔰
Commit: https://github.com/LadybirdBrowser/ladybird/commit/fff09ed3301
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6167
Reviewed-by: https://github.com/tcl3 ✅

Tests/LibWeb/Text/input/interpolation-longhand-properties.html

@@ -34,6 +34,10 @@
                 from: "repeat-x",
                 to: "space",
             },
+            borderRadius: {
+                from: "0px 20px 40px 60px",
+                to: "100px 120px 140px 160px"
+            },
             // by-computed-value properties with 'auto' are discrete
             bottom: {
                 from: "auto",