[wasm][coreclr] First part of the call generator, interp to native

[radekdoulik]

Port of the generator task to the CoreCLR.

It can be now used to update wasm callhelpers manually. Example usage:

./dotnet.sh build /t:RunGenerator /p:GeneratorOutputPath="./" /p:AssembliesScanPath="<your-path-to-assemblies>" src/tasks/WasmAppBuilder/WasmAppBuilder.csproj

The call helper files are split to 2 files, similar as on Mono. The pinvoke/reverse parts of the generator will be updated in the followup PR.

Contributes to #113692

[Copilot]

Pull Request Overview

This PR adds managed-to-native code generation infrastructure for WebAssembly builds, implementing signature mapping and interop thunk generation for both Mono and CoreCLR runtimes.

• Introduces new ManagedToNativeGenerator, SignatureMapper, and InterpToNativeGenerator classes to generate C++ interop code from managed assembly metadata
• Splits the existing callhelpers.cpp into separate files for forward and reverse thunks in CoreCLR
• Adds runtime-flavor-specific compilation support in the build system to maintain separate implementations for Mono and CoreCLR

Reviewed Changes

Copilot reviewed 7 out of 10 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/tasks/WasmAppBuilder/mono/SignatureMapper.cs	Maps .NET types to WASM signature characters (uppercase) for Mono runtime
src/tasks/WasmAppBuilder/mono/ManagedToNativeGenerator.cs	MSBuild task that orchestrates pinvoke and icall scanning/generation for Mono
src/tasks/WasmAppBuilder/mono/InterpToNativeGenerator.cs	Generates C trampoline functions for interpreter-to-native transitions in Mono
src/tasks/WasmAppBuilder/coreclr/SignatureMapper.cs	Maps .NET types to WASM signature characters (lowercase) with additional 'n' type for CoreCLR runtime
src/tasks/WasmAppBuilder/coreclr/ManagedToNativeGenerator.cs	MSBuild task with temporary hardcoded signatures for CoreCLR interop generation
src/tasks/WasmAppBuilder/coreclr/InterpToNativeGenerator.cs	Generates CallFunc_* helper functions for CoreCLR interpreter-to-native calls
src/tasks/WasmAppBuilder/WasmAppBuilder.csproj	Adds conditional compilation to exclude runtime-specific files and defines RunGenerator target
src/coreclr/vm/wasm/callhelpers-reverse.cpp	New file containing reverse thunk implementations for unmanaged-to-managed calls
src/coreclr/vm/wasm/callhelpers-interp-to-managed.cpp	Generated file with signature-specific trampoline functions for interpreter transitions
src/coreclr/vm/CMakeLists.txt	Updates build to reference split callhelpers files instead of single file

[AaronRobinsonMSFT]

/cc @agocke @jkoritzinsky

[radekdoulik]

/ba-g unrelated timeout