fix: Move jest/mock into package build (fix TS under RN 0.87)

[huntie]

Summary

Minimal fix for react-native-safe-area-context compatibility in React Native 0.87 projects. See react-native-community/template#245.

Context

The incoming React Native 0.87 release will ship the Strict TypeScript API by default (moving to a user opt-out).

Typically, this change is scoped to the user's project (@react-native/typescript-config includes skipLibCheck: true) and not library source code.

However, react-native-safe-area-context ships a Jest integration, which is an exception that crosses this boundary:

setupFiles: ['react-native-safe-area-context/jest/mock']

Problem: react-native-safe-area-context/jest/mock pulls ../src/* (of this library) into the scope of the user's TypeScript analysis — instead of the compiled lib/ code, producing a type error against deep imports such as react-native/Libraries/Types/CodegenTypes which no longer resolve (see also #744).

This diff

Fix this types breakage for app consumers, independent of #744.

• Move jest/mock.tsx to src/jest/mock.tsx so builder-bob compiles it like the rest of the library. The react-native-safe-area-context/jest/mock subpath is preserved via shims.
• ✅ Consuming projects now only see this library's .d.ts files, which are exempt from typechecking due toskipLibCheck: false.

Test Plan

• yarn validate:typescript, ESlint, and the Jest suite all pass.
• Simulated an RN 0.88 (main) consumer app with TypeScript 6: published 5.8.0 reproduces the 6 errors from the issue; the packed build from this change typechecks clean.
• Runtime smoke test: The shim loads the compiled mock under Jest, and SafeAreaProvider/useSafeAreaInsets/useSafeAreaFrame render the mock metrics through context.

[huntie]

Note: After #740, we could introduce an "exports" entry to replace these shims (non-breaking).

[janicduplessis]

Do u know what is minimum version of rn / metro that supports exports?

[janicduplessis]

Thanks @huntie !