feat(accessibility): add core types and platform support

[Kyle-Ye]

Summary

• Add shared accessibility values, properties, traits, visibility, activation points, and child behavior storage.
• Add custom content, custom attributes, chart descriptors, data series, and attachment serialization.
• Add platform focus helpers, accessibility SPI and fallback types, and localized system symbol descriptions.
• Move shared numeric and link support into OpenSwiftUICore and document public accessibility APIs.

Related to #1112.

[codecov]

Codecov Report

❌ Patch coverage is 3.30529% with 1609 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.80%. Comparing base (018f209) to head (3ce41ee).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...re/Accessibility/AccessibilityNodeAttachment.swift	0.00%	289 Missing ⚠️
...SwiftUICore/Accessibility/AccessibilityValue.swift	13.16%	244 Missing ⚠️
.../Accessibility/AccessibilityCustomAttributes.swift	0.00%	117 Missing ⚠️
...wiftUICore/Accessibility/AccessibilityTraits.swift	0.00%	117 Missing ⚠️
...ore/Accessibility/AccessibilityCustomContent.swift	0.00%	94 Missing ⚠️
...UICore/Accessibility/AccessibilityProperties.swift	0.00%	89 Missing ⚠️
...UICore/Accessibility/AccessibilityDataSeries.swift	0.00%	74 Missing ⚠️
...e/Accessibility/AccessibilityChartDescriptor.swift	0.00%	73 Missing ⚠️
...Accessibility/AccessibilityNullableOptionSet.swift	0.00%	58 Missing ⚠️
...rces/OpenSwiftUICore/Util/AccessibilityShims.swift	0.00%	58 Missing ⚠️
... and 17 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1114      +/-   ##
==========================================
- Coverage   33.70%   32.80%   -0.91%     
==========================================
  Files         799      822      +23     
  Lines       62211    66340    +4129     
==========================================
+ Hits        20969    21762     +793     
- Misses      41242    44578    +3336     

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[tuist]

🛠️ Tuist Run Report 🛠️

Tests 🧪

Scheme	Status	Ran test modules	Commit
OpenSwiftUI	✅	7	17abd6a49

Builds 🔨

Scheme	Status	Duration	Commit
OpenSwiftUI	✅	52.6s	17abd6a49