Add XCFramework build script and publish release workflow

[Kyle-Ye]

Summary

• Add Scripts/build_xcframework.sh for building xcframeworks directly from Package.swift via xcodebuild archive + xcodebuild -create-xcframework
• Add publish_release.yml GitHub Actions workflow triggered on release tags and manual dispatch
• Fix swiftinterface leaks and library evolution issues for xcframework consumers

Close #836

Build Script

• Supports --sdk, --archs, and --debug CLI options
• Builds main OpenSwiftUI.xcframework plus stub xcframeworks for dependency modules (OpenSwiftUICore, OpenAttributeGraphShims, OpenCoreGraphicsShims, OpenObservation, OpenQuartzCoreShims, OpenRenderBoxShims)
• Stub xcframeworks contain only swiftmodule/swiftinterface (code is statically linked into main framework)
• Default SDKs: macosx and iphonesimulator. iphoneos support blocked by AG issue (Add iOS device support for OpenSwiftUI #835)

Fixes

• Fix OpenAttributeGraphShims import leak in swiftinterface (@_spiOnly)
• Fix OpenSwiftUI_SPI depending on OpenRenderBox instead of OpenRenderBoxShims
• Guard UIFoundation_Private import with OPENSWIFTUI_XCFRAMEWORK_BUILD
• Fix PreviewShims opaque return types for library evolution
• Fix Never+View Body typealias for swiftinterface rebuild
• Fix macOS framework bundle structure for codesigning
• Work around xcodebuild SPM macro bug for non-macOS SDKs (Add xcframework support #836)

Test Plan

• Build xcframeworks with bash Scripts/build_xcframework.sh OpenSwiftUI
• Integrate into consumer Xcode project (ImageDemo)
• Verify compile + link + launch on iOS Simulator
• Verify compile + link + launch on macOS
• Verify codesigning works for all stub frameworks

[augmentcode]

🤖 Augment PR Summary

Summary: Adds automation for producing and publishing OpenSwiftUI XCFramework artifacts, while tightening module interfaces for XCFramework consumers.

Changes:

• Introduces Scripts/build_xcframework.sh to archive an SPM scheme per SDK/arch and assemble a primary OpenSwiftUI.xcframework.
• Generates stub XCFrameworks for dependency modules (module interfaces only) to satisfy public .swiftinterface references.
• Adds a publish_release.yml workflow to build, zip, compute checksums, and attach XCFrameworks to GitHub Releases (or upload as artifacts on manual runs).
• Updates Package.swift RenderBox wiring and adjusts target settings to match the shims-based dependency layout.
• Fixes swiftinterface “leaks” via @_spiOnly imports and guards private framework imports during XCFramework builds.
• Adjusts preview shims to avoid opaque return types in public API and adds an XCFramework-build workaround for an SPM macro build issue.

Technical Notes: The build path uses xcodebuild archive + -create-xcframework, copies Swift module artifacts into frameworks, strips private/package interfaces by default, and includes dSYMs in slices where available.

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[augmentcode]

Review completed. 2 suggestions posted.

Comment augment review to trigger a new review at any time.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 26.93%. Comparing base (1fa5257) to head (7160e6b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #838      +/-   ##
==========================================
- Coverage   27.01%   26.93%   -0.08%     
==========================================
  Files         666      671       +5     
  Lines       42826    43332     +506     
==========================================
+ Hits        11568    11671     +103     
- Misses      31258    31661     +403     

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