refactor(app): move to TypeScript

[russellwheatley]

Description

• Created an index.ts which exports for consumers only, separated modular in modular.ts and namespaced.ts for separation of concerns.
• Created a types/app.ts for consumer types, and types/internal.ts for internal implementation types.
• Updated paths in package.json to allow peer dependencies (i.e. other RNFB packages) to maintain access to internal and common API.
• Updated other packages that already use typescript to ensure they can still access app package internal API (common/ and internal/).
• Refactored functions, removed types.d.ts file and put in types/functions.ts like app package.
• Fixed type-tests.ts for app and functions packages. We only include these two packages as all the other package types need updating as they're full of errors: https://github.com/invertase/react-native-firebase/blob/refactor-app-typescript/tsconfig.json#L2. Intellisense now works for these two packages, PR for the rest of the packages: refactor: improved exported types and updated type-tests.ts, intellisense now works #8805

Related issues

Release Summary

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • Android
  • iOS
  • Other (macOS, web)
• My change includes tests;
  • e2e tests added or updated in packages/\*\*/e2e
  • jest tests added or updated in packages/\*\*/__tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

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