[Cashtab] Convert wallet context to ts

Summary:
Troubleshooting load speed issues in Cashtab. Need to get typescript at the highest level so I can find any mismatches. Start here.

Cashtab screens load important wallet information from Context. But, because type definitions have not been applied there, we aren't really getting a lot of typescript benefits on our screens.

Implement typescript on context file and at entry point of app. This required also implementing it in our GoogleAnalytics, which is loaded from this screen. We also see many "lint-like" changes in tsx files of app screens -- this is because, before context was updated, they were not actually getting the types of wallet context.

With typescript, implement improved condition check on context loading.

This is part of a broader effort to debottleneck Cashtab load times.

Test Plan: npm test, arc lint no ts errors

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D17288