[XABT] GeneratePackageManagerJava - Convert NativeCodeGenState to Cecil-less DTOs.

[jpobst]

Context: #10062

One issue with our desire to move around LLVM Marshal Method build code so that it can work with Ready2Run is that our current implementation relies on holding Cecil AssemblyDefinition objects open in global state across multiple targets. While these objects are open, no other process can access our assemblies, making it harder to reorder targets and tasks.

As a first step towards refactoring this process, let's move the data into a DTO that does not require Cecil. Additionally, this makes it clear what data is actually consumed by <GeneratePackageManagerJava> rather than "entire assemblies" so we can focus on how to properly obtain and persist the data.

This still relies on BuildEngine4.RegisterTaskObject to store the data, but a likely future step would be to persist it to a file instead.

[Copilot]

Pull Request Overview

This pull request refactors the way marshal method data is stored by converting the Cecil-dependent NativeCodeGenState into Cecil‐less DTOs, improving task decoupling and assembly access.

• Updated various classes and method signatures in MarshalMethodsNativeAssemblyGenerator.cs to work with the new DTO types.
• Introduced MarshalMethodCecilAdapter.cs to convert Cecil objects into DTOs and updated related build task registrations in GeneratePackageManagerJava.cs and GenerateMainAndroidManifest.cs.
• Defined a new task constant in GenerateJavaStubs.cs to support the DTO-based state transfer.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Xamarin.Android.Build.Tasks/Utilities/MarshalMethodsNativeAssemblyGenerator.cs	Updated method signatures and type references to use DTO types instead of Cecil objects.
src/Xamarin.Android.Build.Tasks/Utilities/MarshalMethodCecilAdapter.cs	Added adapter methods to create DTOs; note issues with dictionary initializers.
src/Xamarin.Android.Build.Tasks/Tasks/GeneratePackageManagerJava.cs	Modified retrieval and usage of NativeCodeGenState to use the new DTO type.
src/Xamarin.Android.Build.Tasks/Tasks/GenerateMainAndroidManifest.cs	Transferred and disposed the Cecil-dependent state appropriately after conversion.
src/Xamarin.Android.Build.Tasks/Tasks/GenerateJavaStubs.cs	Added a new task key to facilitate registration of the DTO-based state.

[jonathanpeppers]

This makes sense to me as the first step.

My comments aren't super important, especially if some of that code will be different in future PRs.