Add visionOS unit tests, unit test targets, test app, testing host app, and xcconfigs

[mipetriu]

Proposed changes

This PR adds a visionOS test app in MSAL mostly taken from the publicly available iOS Graph API sample. Keeping these files separate should allow for more simple review of the overall visionOS changes needed in MSAL: https://github.com/AzureAD/microsoft-authentication-library-for-objc/pull/1990

Type of change

• [x] Feature work
• [ ] Bug fix
• [ ] Documentation
• [ ] Engineering change
• [ ] Test
• [ ] Logging/Telemetry

Risk

• [ ] High – Errors could cause MAJOR regression of many scenarios. (Example: new large features or high level infrastructure changes)
• [x] Medium – Errors could cause regression of 1 or more scenarios. (Example: somewhat complex bug fixes, small new features)
• [ ] Small – No issues are expected. (Example: Very small bug fixes, string changes, or configuration settings changes)

Additional information

[frogcjn]

I have improved the xcconfig parts for visionOS and building XCFramework process which developer could build themselves swift package version of MSAL, you could check the pull request at https://github.com/AzureAD/microsoft-authentication-library-for-objc/pull/2065