Convert more COM interop MethodDescCallSite to UnmanagedCallersOnly (UCO)

[Copilot]

Continues the COM interop UCO migration (group 5), converting three MethodDescCallSite call sites to the UCO pattern and removing associated dead code. Addresses all pending feedback from #125508.

Changes

New UCO helpers in StubHelpers.cs

• GetDispatchExPropertyFlags – replaces two MethodDescCallSite calls for PropertyInfo.CanRead/CanWrite in DispatchEx_GetMemberProperties
• CallICustomQueryInterface – replaces the InvokeICustomQueryInterfaceGetInterface_CallBack struct/callback pattern; returns int directly (uses InvokeThrowing_Ret)
• InvokeConnectionPointProviderMethod – replaces two MethodDescCallSite calls in ConnectionPoint::InvokeProviderMethod; always uses nint for the delegate ctor (drops useUIntPtrCtor bool per feedback)
• Added [RequiresUnsafe] to the existing GetIEnumeratorToEnumVariantMarshaler UCO overload for consistency

Feedback addressed from #125508

• INVOKE_CONNECTION_POINT_PROVIDER_METHOD registered as NoSig in corelib.h (has unmanaged fn-ptr params — encoding in metasig not worth the pain)
• CallICustomQueryInterface uses InvokeThrowing_Ret<INT32> and passes ppUnkOut directly — no local copy needed
• useUIntPtrCtor bool removed — delegate ctors always have an (object, nint) overload

Dead code removed

• InvokeICustomQueryInterfaceGetInterface_CallBack + arg struct in comcallablewrapper.cpp
• GetICustomQueryInterfaceGetInterfaceMD / m_pICustomQueryInterfaceGetInterfaceMD from ComCallWrapperTemplate
• m_ohDelegate union field and GetOHDelegate/SetOHDelegate/GetObjCreateDelegate/SetObjCreateDelegate from EEClass/MethodTable — SetObjCreateDelegate had no callers; the delegate-based CreateAggregatedInstance path was effectively dead

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[Copilot]

Pull request overview

This PR continues the CoreCLR COM interop migration away from MethodDescCallSite toward the UnmanagedCallersOnly (UCO) reverse-P/Invoke calling pattern, and removes now-dead COM interop callback/delegate infrastructure in the VM.

Changes:

• Added new UCO helpers in StubHelpers.cs and updated native call sites to use UnmanagedCallersOnlyCaller.
• Converted COM interop call paths in stdinterfaces.cpp, comconnectionpoints.cpp, and comcallablewrapper.cpp from MethodDescCallSite to UCO-based helpers.
• Removed dead COM interop delegate/callback code paths and related cached fields/helpers in VM types.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/coreclr/vm/stdinterfaces.cpp	Uses UCO helper to query PropertyInfo.CanRead/CanWrite flags instead of two MethodDescCallSite calls.
src/coreclr/vm/runtimecallablewrapper.cpp	Removes unused delegate-based aggregated COM instance creation path and related logic.
src/coreclr/vm/methodtable.h	Removes delegate-handle-related APIs from MethodTable.
src/coreclr/vm/methodtable.cpp	Removes implementations for COM object-creation delegate storage/retrieval.
src/coreclr/vm/metasig.h	Adds COM-interp UCO metasig definitions for new StubHelpers methods.
src/coreclr/vm/corelib.h	Registers new StubHelpers methods (including a NoSig entry).
src/coreclr/vm/comconnectionpoints.cpp	Uses a single UCO helper to construct delegate + invoke provider method.
src/coreclr/vm/comcallablewrapper.h	Removes cached ICustomQueryInterface.GetInterface MethodDesc field/API.
src/coreclr/vm/comcallablewrapper.cpp	Replaces callback/cached-MD pattern with UCO helper that calls ICustomQueryInterface.GetInterface.
src/coreclr/vm/class.h	Removes now-dead delegate handle storage from EEClass COM interop union.
src/coreclr/System.Private.CoreLib/src/System/StubHelpers.cs	Adds UCO helpers for DispatchEx property flags, ICustomQueryInterface, and connection point invocation.

[Copilot]

The DispatchExPropertyCanRead/DispatchExPropertyCanWrite bit values are duplicated here and in StubHelpers.GetDispatchExPropertyFlags. Consider centralizing them (e.g., a shared header/enum or a single source of truth) or at least adding a note/assertion to keep the native and managed definitions in sync to prevent silent flag drift.