script: Impl safe from_jsval wrapper (#38149)

Implement `SafeFromJSValConvertible`, a safe wrapper for
`ToJSValConvertible`. And, replace unsafe `ToJSValConvertible` with
`SafeFromJSValConvertible` in `script/dom` to reduce the amount of
unsafe code in `script`.

This would support the implementation of `AdoptedStylesheet` where we
will need to have a setter/getter of sequence, that was implemented by
`any` types.

Part of https://github.com/servo/servo/issues/37951

Signed-off-by: Jo Steven Novaryo <jo.steven.novaryo@huawei.com>

components/script_bindings/conversions.rs

@@ -79,6 +79,30 @@ impl ToJSValConvertible for DOMString {
     }
 }
 
+/// A safe wrapper for `FromJSValConvertible`.
+pub trait SafeFromJSValConvertible: Sized {
+    type Config;
+
+    #[allow(clippy::result_unit_err)] // Type definition depends on mozjs
+    fn safe_from_jsval(
+        cx: SafeJSContext,
+        value: HandleValue,
+        option: Self::Config,
+    ) -> Result<ConversionResult<Self>, ()>;
+}
+
+impl<T: FromJSValConvertible> SafeFromJSValConvertible for T {
+    type Config = <T as FromJSValConvertible>::Config;
+
+    fn safe_from_jsval(
+        cx: SafeJSContext,
+        value: HandleValue,
+        option: Self::Config,
+    ) -> Result<ConversionResult<Self>, ()> {
+        unsafe { T::from_jsval(*cx, value, option) }
+    }
+}
+
 // https://heycam.github.io/webidl/#es-DOMString
 impl FromJSValConvertible for DOMString {
     type Config = StringificationBehavior;