[clr-ios] Update AppleAppBuilder to support dynamic R2R images

[kotlarmilos]

Description

Integrate Mach-O objects produced by Crossgen2 into the Apple app build. Ensure the .o files are linked into a dylib, correctly referenced by the app, signed, packaged into the .app bundle, and accompanied by debug symbols. Cache composite R2R outputs in Debug to speed up incremental builds.

Tasks:

• Add an MSBuild task/target that links Crossgen2 .o into a .dylib
  • Accept multiple .o inputs and emit a single composite R2R .dylib
• Link the app with:
  • libcoreclr.dylib via @rpath
  • The composite R2R .dylib produced above
  • Ensure @rpath entries include @executable_path/Frameworks
• Place the composite R2R .dylib in the bundle
• Generate debug symbols (.dSYM) for both the app and the composite R2R .dylib
• Sign the app and all embedded dylibs
• Implement Debug build caching for R2R artifacts
  • Persist composite R2R inputs/outputs under an incremental cache key
  • Reuse cached .o and .dylib when inputs are unchanged
• Add CI validation step to verify dylib presence, code signature and rpath load commands

DoD: The Apple build produces a signed dylib inside the .app bundle.

[dotnet-policy-service]

Tagging subscribers to 'os-ios': @vitek-karas, @kotlarmilos, @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to this area: @BrzVlad, @janvorli, @kg
See info in area-owners.md if you want to be subscribed.