Add support for host callback to get information for platform-native composite R2R images

[elinor-fung]

Depends on #120777. (First commit is a merge from that PR)

Add the basic runtime flow for calling into the host to get information about a platform-native R2R - see ReadyToRun Platform Native Envelope.

• Add get_native_code_data callback to host_runtime_contract
• If a component R2R assembly has READYTORUN_FLAG_PLATFORM_NATIVE_IMAGE, invoke the callback to get the R2R header, image size, and image base address
• Currently only implemented and tested on Windows (with local changes to include the flag)
• Mach-O support will need Add support for emitting Mach-O R2R images #121186

Contributes to #120065.

[jkoritzinsky]

cc: @adamperlin

[elinor-fung]

This should be ready for review now.

[Copilot]

Pull Request Overview

This PR adds support for platform-native R2R (ReadyToRun) composite image loading, enabling the runtime to load composite R2R images in native platform formats (e.g., Mach-O on macOS, PE on Windows) through a new host contract callback mechanism.

Key changes:

• New host contract callback get_native_code_data to retrieve platform-native composite images from the host
• New READYTORUN_FLAG_PLATFORM_NATIVE_IMAGE flag to mark component assemblies
• Test infrastructure to validate platform-native R2R composite image loading

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/native/corehost/host_runtime_contract.h	Adds new structs and callback interface for native code data retrieval
src/installer/tests/Assets/Projects/HostApiInvokerApp/HostRuntimeContract.cs	Updates managed representation of host contract with new callback
src/coreclr/inc/readytorun.h	Defines new READYTORUN_FLAG_PLATFORM_NATIVE_IMAGE flag
src/coreclr/inc/hostinformation.h	Declares GetNativeCodeData helper method
src/coreclr/vm/hostinformation.cpp	Implements GetNativeCodeData to call host callback
src/coreclr/vm/readytoruninfo.cpp	Passes platform-native flag when loading composite images
src/coreclr/vm/assemblybinder.h	Adds isPlatformNative parameter to LoadNativeImage
src/coreclr/vm/assemblybinder.cpp	Simplifies LoadNativeImage and passes isPlatformNative flag
src/coreclr/vm/nativeimage.h	Updates Open signature with componentModulePath and isPlatformNative
src/coreclr/vm/nativeimage.cpp	Refactors to support both host callback and PE-based loading paths
src/coreclr/hosts/corerun/corerun.hpp	Adds platform-specific helpers for UTF-8 conversion and image introspection
src/coreclr/hosts/corerun/corerun.cpp	Implements get_native_code_data callback for testing
src/tests/Loader/PlatformNativeR2R/PlatformNativeR2R.csproj	Test project configuration
src/tests/Loader/PlatformNativeR2R/PlatformNativeR2R.cs	Test implementation using R2RDump validation

[elinor-fung]

/ba-g Android timeouts