[Cashtab] If user selects a non-active wallet in webapp select prompt, activate that wallet

Summary:
We have a workflow problem now

• user connects cashtab web wallet to a mobile app
• they are prompted with a list of their wallets to choose
• if they choose the non active wallet and import it, the app imports it, but will still open the unselected wallet

this means users can accidentally send txs with the wrong wallet

So, before closing the tab, we ensure the selected wallet is activated.

We will do something similar with the extension but the logic there is distinct and should be handled in its own diff

T3876

Test Plan: npm test, use in webapp tests with cashtab.io in scenario described above, works

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18589