Adjust the method for UITableViewCell separator hiding to prevent hangs

[lukas-cap]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

Turns out that the method I previously implemented to keep separator insets at zero frame actually may not work, and can cause a hang because the system sometimes adds its own inset to whatever inset the client sets.

Let's change the logic to:

1. Only set the inset once, not piece-meal
2. Loosen up the condition to cover cases where after setting, the inset may actually be bigger than intended (which is still fine for our purposes).

Binary change

N/A

Verification

Sanity in test app that insets are still gone and view debugger still doesn't crash.

Pull request checklist

This PR has considered:

• Light and Dark appearances
• iOS supported versions (all major versions greater than or equal current target deployment version)
• VoiceOver and Keyboard Accessibility
• Internationalization and Right to Left layouts
• Different resolutions (1x, 2x, 3x)
• Size classes and window sizes (iPhone vs iPad, notched devices, multitasking, different window sizes, etc)
• iPad Pointer interaction
• SwiftUI consumption (validation or new demo scenarios needed)
• Objective-C exposure (provide it only if needed)

Microsoft Reviewers: Open in CodeFlow