Use the @ethvault/iframe-provider-polyfill to support iframe wallets

[moodysalem]

See #388 for context

[moodysalem]

It looks like the package @ensdomains/ui contains the web3 setup code. It doesn't look like a user choice AFAICT. I can add the following to that package in setupWeb3, if preferable:

• check if window is in iframe
• • if in iframe, try creating an iframe provider with a target origin of 'https://ethvault.xyz'
• • try to enable the iframe provider via await iframeProvider.enable()
• • • if enable succeeds, set window.ethereum and window.web3 to iframeProvider
• • • if enable fails or takes longer than 1 second, do nothing
• if not in iframe, do nothing

Since it's shared code, it would enable the provider in all the ENS apps that use it.

[moodysalem]

I will pursue an audit via EthereumCommonwealth/Auditing#351

[moodysalem]

Here is that alternative implementation
ensdomains/ui#18

[makoto]

Duplicate to #421