Fix COM interface method calling wrong method for base/derived classes

[elinor-fung]

When a COM interface is implemented by a class with a virtual method and a derived class overrides it, they share a ComMethodTable. With #126002, when a ComMethodTable lay out happens, we resolve each interface method into its target method and create a corresponding UMEntryThunkData. This means that if a derived class is used first, its override gets baked into the layout, so the base class will call the wrong method - and vice versa if the base class is used first.

This change prevents sharing of a ComMethodTable between a base/derived class if the actual targets of any interface method differ.

Found while investigating #127512.

cc @dotnet/appmodel @AaronRobinsonMSFT

Example setup:

[ComVisible(true)]
public interface IFoo
{
    void DoWork();
}
 
[ComVisible(true), ComDefaultInterface(typeof(IFoo))]
public class Base : IFoo
{
    public virtual void DoWork() { }
}
 
[ComVisible(true), ComDefaultInterface(typeof(IFoo))]
public class Derived : Base
{
    public override void DoWork() { }
}

If Derived is created first, calling Base.DoWork calls Derived.DoWork.

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[Copilot]

Pull request overview

This PR adjusts CoreCLR COM callable wrapper (CCW) vtable sharing behavior so that a derived type cannot reuse a parent’s ComMethodTable when any interface method would resolve to a different target MethodDesc, and adds a regression test covering base-first vs derived-first COM access order.

Changes:

• Add a new COM interop regression test that calls interface methods via the COM vtable and asserts the correct base/derived override is invoked independent of access order.
• Replace the prior “same slots as parent” check with a stricter shareability check that also compares resolved dispatch targets (MethodDesc*) between parent and child.
• Remove the now-unused MethodTable::ImplementsInterfaceWithSameSlotsAsParent helper.

Show a summary per file

File	Description
src/coreclr/vm/comcallablewrapper.cpp	Adds CanShareComMethodTableWithParent and uses it to gate parent ComMethodTable reuse based on resolved targets.
src/coreclr/vm/methodtable.h	Removes declaration of ImplementsInterfaceWithSameSlotsAsParent.
src/coreclr/vm/methodtable.cpp	Removes implementation of ImplementsInterfaceWithSameSlotsAsParent.
src/tests/Interop/COM/VirtualMethodOverride/VirtualMethodOverrideTest.csproj	Adds a new COM interop test project for the regression scenario.
src/tests/Interop/COM/VirtualMethodOverride/VirtualMethodOverrideTest.cs	Adds regression coverage for correct dispatch to base vs derived overrides when COM access order differs.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 2

[AaronRobinsonMSFT]

Why does it being NULL make this an issue?

[Copilot]

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 0 new