ohos: Use QNapi eval() instead of call() in the WebView plugin

QNapi::Object::call() and QNapi::Reference<QNapi::Object>::call() are
scheduled for deprecation, so replace their uses in the plugin with
eval().

Task-number: QTBUG-146838
Pick-to: 6.12
Change-Id: Id3ac66f6e02e3ed55ceac3c7f29d9c8c3efe394d
Reviewed-by: SanthoshKumar Selvaraj <santhosh.kumar.selvaraj@qt.io>
Reviewed-by: Zbigniew Chyla <zbigniew.chyla@qt.io>