chore: manually mask swiftui views

[marandaneto]

:bulb: Motivation and Context

Alternative solution for https://github.com/PostHog/posthog-ios/issues/162 You inject a synthetic view into the marked view and get the X and Y positions based on that component. You don't have access to the original view but you know where it should be masked.

:green_heart: How did you test it?

:pencil: Checklist

• [x] I reviewed the submitted code.
• [ ] I added tests to verify the changes.
• [x] I updated the docs if needed.
• [x] No breaking change or entry added to the changelog.

[marandaneto]

@ioannisj you can pick this up if you wish, the PoC works, just need to polish and finish it

[ioannisj]

• Updated relevant documentation under this PR
• Replaced PostHogScreenshotMasker with an associated UIView property phIsManuallyMasked which is then grabbed during findMaskableWidgets call

[marandaneto]

@ioannisj I cannot approve my own PR so feel free to get it approved/merged after fixing the conflicts.