Records may only have String keys

[unadlib]

Describe the bug
According to proposal-record-tuple, the key of Record can only be a string.

Records may only have String keys, not Symbol keys, due to the issues described in tc39/proposal-record-tuple#15. Creating a Record with a Symbol key is a TypeError.

To Reproduce

const record = #{ [Symbol()]: #{} };

Expected behavior
It should show the error // TypeError: Record may only have string as keys