LibWeb: Add support for indexed setter of HTMLOptionsCollection

Author: https://github.com/vpzomtrrfrt
Commit: 99824eae14
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/630
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/tcl3 ✅

Tests/LibWeb/Ref/options-set-index.html

@@ -0,0 +1,7 @@
+<link rel="match" href="reference/options-set-index.html" />
+<select id="select"></select>
+<script>
+    const select = document.getElementById("select");
+    select.options[0] = new Option("text");
+    select.value = "text";
+</script>

Tests/LibWeb/Ref/reference/options-set-index.html

@@ -0,0 +1 @@
+<select><option>text</option></select>