Web3.givenProvider is undefined

[brunobar79]

This is happening with Web3 1.2+
I was able to reproduce it on spankchain.

[brunobar79]

From what I can tell, we won't be able to fix this: https://github.com/ethereum/web3.js/blob/a5e832fc20088cf4c4e916bc0ec3107ceb4428d0/packages/web3-core-requestmanager/src/givenProvider.js#L37

It looks like the givenProvider detection is happening as early as the library loads, what makes impossible for mobile to get the provider ready that early.

I guess the only thing we can do is to discourage the usage of Web3.givenProvider, and use window.ethereum instead.

This should be mentioned in #340