Update Account Linking Docs for Cadence 1.0 and better error messages

[joshuahannan]

Issue to be solved

Some of the explanations and cadence code in the account linking docs has not be reviewed and updated to Cadence 1.0 yet.

Suggest A Solution

Go through that section of the docs and read it to make sure all the descriptions make sense with the latest understanding of Cadence and account linking and that the Cadence code is all updated to Cadence 1.0 syntax, best practices, and uses descriptive error messages as described in this issue

Additional pages that have to do with account linking that need to be updated:

• https://github.com/onflow/docs/blob/main/docs/build/guides/mobile/walletless-pwa.md