New force-sync method (load-capped) to track bad experiences that might lead users to leave/delete app (improved churn tracking)

[Jeehut]

Individual commits:

• Update checks for temporary name xrOS to final visionOS
• Simple patch to ensure nothing is logged in SwiftUI preview mode
• Refactor some function & property naming in SignalManager for more clarity + update docs
• React to background/foreground changes on visionOS
• Add new method TelemetryClient.requestImmediateSync() for advanced churn optimization

Some functions in SignalManager seemed to have been named after planned behavior that was never implemented. Therefore, the function names & docs were somewhat misleading. I adjusted the names to reflect what they actually do.

The new method .requestImmediateSync() fixes #130 and should only be used in rare cases where important information is sent to the servers that must reach the servers even if the user might leave the app right after and never return. This can be useful for apps that are used only once to track important last steps of the user. Or for experiences like errors that could make the user delete the app right after. Those error signals would never reach the server without this.

This PR also fixes #134 (a minor SwifUI logging issue). It also fixes some warnings regarding visionOS (instead of xrOS) & improves Vison Pro support.

[winsmith]

I love this!