Cleanup multicast delegate handling

[MichalPetryka]

Builds on previous PRs.

Switches multicast to Wrapper[], cleans up and spanifies combine/remove.

Cleans up code after the moves and type changes.

cc @jkotas @tannergooding

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[MichalPetryka]

@MihuBot -nuget

[Copilot]

Pull request overview

This PR refactors CoreCLR multicast delegate internals to store invocation lists as a strongly-typed Delegate.Wrapper[] instead of object[], and updates the VM-side multicast invoke stub generation accordingly. The change primarily aims to simplify/“spanify” combine/remove paths and reduce reliance on object[]-based casting.

Changes:

• Switch multicast invocation list storage from object[] to Delegate.Wrapper[] in CoreLib, updating TryGetInvocations, GetInvocationList, Target, GetMethodImpl, CombineImpl, and RemoveImpl.
• Update the VM multicast invoke IL stub to index a Wrapper[] (via ldelema) and then load the wrapped delegate (ldfld Value).
• Add CoreLib binder entries for System.Delegate+Wrapper and its Value field for the stub generator.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/coreclr/vm/corelib.h	Adds CoreLibBinder definitions for Delegate+Wrapper and Wrapper.Value.
src/coreclr/vm/comdelegate.cpp	Updates multicast invoke stub IL emission to load delegates out of Wrapper[] via ldelema + ldfld.
src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs	Implements Wrapper[]-based multicast storage and span-based combine/remove/equality/hash code paths.

[jkotas]

@EgorBot

using System;
using BenchmarkDotNet.Attributes;

public class Test
{
    private Action _a, _b;

    [GlobalSetup]
    public void GlobalSetup()
    {
        _a = new Action(new Test().GlobalSetup) + new Action(new Test().GlobalSetup);
        _b = new Action(new Test().GlobalSetup) + new Action(new Test().GlobalSetup);
    }

    [Benchmark]
    public bool Equals() => _a.Equals(_b);
}

[jkotas]

Thank you!

[jkotas]

/ba-g known failure that has been fixed in main already