Update methods on Frame type to return Promises

[allansson]

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[inancgumus]

Thanks 🙇 🎉

[ankur22]

LGTM. I think we will might need to revisit it though if some of the APIs change a tiny bit. E.g. textContext currently only returns string from the browser module, but we may change that to also return null when string is empty.

[inancgumus]

LGTM. I think we will might need to revisit it though if some of the APIs change a tiny bit. E.g. textContext currently only returns string from the browser module, but we may change that to also return null when string is empty.

Added this as a task here grafana/xk6-browser#1302