feat: initial_checked attribute for inputs (#1540)

Mapped to defaultChecked property of HTMLInputElement.

packages/html/src/elements.rs

@@ -1107,6 +1107,7 @@ builder_constructors! {
         formnovalidate: Bool DEFAULT,
         formtarget: Target DEFAULT,
         height: isize DEFAULT,
+        initial_checked: Bool DEFAULT,
         list: Id DEFAULT,
         max: String DEFAULT,
         maxlength: usize DEFAULT,