fix: renderRouter on windows

[marklawlor]

Why

Fix: #24493
Fix: https://linear.app/expo/issue/ENG-10196

How

Metro expects all paths to be posix, but the require.context ponyfill keeps the windows separators. This PR ensures the filenames use posix seperators

Test Plan

Tested using the repo provided in the linked issue on windows 11.

Checklist

• Documentation is up to date to reflect these changes (eg: https://docs.expo.dev and README.md).
• Conforms with the Documentation Writing Style Guide
• This diff will work correctly for npx expo prebuild & EAS Build (eg: updated a module plugin).

[linear]

ENG-10196 Routing fails with renderRouter on Windows

This issue was automatically imported from GitHub: #24493

Issue accepted by mark

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Summary:

• The user is facing an issue where routing to 'content' fails for tests on a Windows environment. The same tests pass successfully on Linux.
• The issue is apparent when using renderRouter. When performing tests, the routing failure leads to an 'Unmatched Route' result. However, when running the app on a device, everything appears to work as intended.
• The user provides the error message that occurs when the test fails, suggesting the source of the issue may be related to routing.
• In a larger project, they also experience a warning message that includes \\ in paths, which could suggest a problem with path handling on Windows.
• The same problem does not occur on Linux, suggesting that this is a platform-specific issue.