Implement PlatformView features and ViewRendererHost improvements

[Kyle-Ye]

Summary

Close #517

Changes

• Update PlatformViewChild
  • Fix missing update call for Representable types)
  • Implement ViewRendererHost.enclosingHosts
  • Implement PlatformView.isPlatformFocusContainerHost
  • Correct signpost implementation
• Update UnsafePointer usage

[codecov]

Codecov Report

❌ Patch coverage is 0% with 149 lines in your changes missing coverage. Please review.
✅ Project coverage is 24.53%. Comparing base (5281451) to head (7473ebd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...esentable/Platform/PlatformViewRepresentable.swift	0.00%	124 Missing ⚠️
.../OpenSwiftUICore/View/Graph/ViewRendererHost.swift	0.00%	9 Missing ⚠️
.../OpenSwiftUICore/Data/Util/ScrapeableContent.swift	0.00%	6 Missing ⚠️
...tUICore/Render/RendererEffect/RendererEffect.swift	0.00%	6 Missing ⚠️
Sources/OpenSwiftUI/Event/Focus/FocusGroup.swift	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #557      +/-   ##
==========================================
- Coverage   24.63%   24.53%   -0.11%     
==========================================
  Files         505      506       +1     
  Lines       29204    29319     +115     
==========================================
- Hits         7195     7194       -1     
- Misses      22009    22125     +116     

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