Add Xcode 27 SDK support

[Kyle-Ye]

Summary

• Add SDK-version addition guards for Xcode 26 and Xcode 27 availability surfaces.
• Update UIFoundation paragraph style shims to match SDK 27 public definitions.
• Keep compatibility with Xcode 26.3 / macOS 26.2 SDK by only exposing SDK 27 additions when the SDK defines them.
• Document the Xcode 27 / SDK 27 compatibility update in the toolchain changelog.

Validation

• Xcode 27 / macOS 27: AppKit + UIFoundation_Private import typecheck.

• Xcode 26.3 / macOS 26.2: AppKit + UIFoundation_Private import typecheck.

• Xcode 26.3 / macOS 26.2:

  DEVELOPER_DIR=/Applications/Xcode-26.3.0.app/Contents/Developer swift build --target OpenSwiftUI_SPI --build-path .build/xcode26_3_spi_base_sdk_macros

• Xcode 27 and Xcode 26.4.1 iOS SDKs: UIKit + UIFoundation_Private import typecheck.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 26.71%. Comparing base (a3e0c8d) to head (2d05a6e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #902   +/-   ##
=======================================
  Coverage   26.71%   26.71%           
=======================================
  Files         697      697           
  Lines       48916    48916           
=======================================
+ Hits        13067    13068    +1     
+ Misses      35849    35848    -1     

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[augmentcode]

🤖 Augment PR Summary

Summary: Adds Xcode 27 / SDK 27 compatibility guards and updates UIFoundation shims to match newer public SDK surfaces.

Changes:

• Introduce OPENSWIFTUI_HAS_SDK_26_ADDITIONS and OPENSWIFTUI_HAS_SDK_27_ADDITIONS macros in OpenSwiftUIBase.h based on SDK max-allowed version checks.
• Gate new SDK 27 declarations in NSParagraphStyle.h (e.g., NSTextTab alignment APIs, paragraph alignment/textBlocks, and macOS-only paragraph fields).
• Add an NSTextAlignment shared-section shim in NSText.h to align with SDK 27 definitions.
• Switch NSStringDrawingOptions SDK-26 gating to use the new macro for cleaner, centralized checks.

Technical Notes: The new guards keep Xcode 26.x builds working by compiling SDK 27 additions only when the underlying SDK exposes the relevant availability macros.

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[augmentcode]

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