[cDAC] Preserve basic object type input

[rcj1]

This is an inout param. Found via assert in an internal diagnostic test.

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[Copilot]

Pull request overview

This PR fixes GetBasicObjectInfo to treat pObjTypeData as a true in/out parameter by preserving the caller-provided struct contents on failure (e.g., invalid object references), aligning behavior with the intended contract for this API.

Changes:

• Stop zeroing *pObjTypeData at the start of DacDbiImpl.GetBasicObjectInfo, so caller-initialized type info isn’t clobbered when the reference is invalid.
• Update the IDacDbiInterface::GetBasicObjectInfo IDL signature to mark pObjTypeData as [in, out] rather than [out].

Show a summary per file

File	Description
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs	Preserves the caller-provided DebuggerIPCE_ExpandedTypeData when the object reference is invalid.
src/coreclr/inc/dacdbi.idl	Updates the IDL contract to reflect pObjTypeData as an in/out parameter.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1

[Copilot]

Copilot's findings

Suppressed comments (1)

src/coreclr/debug/inc/dacdbiinterface.h:1698

• The comment and IDL now describe pObjTypeData as an in/out parameter, but the C++ interface signature still annotates it as OUT. That makes the contract inconsistent and can mislead call sites and reviewers about whether the incoming contents must be preserved/considered. Update the signature to drop the OUT annotation (or otherwise mark it in/out) for pObjTypeData.

    //     in/out: pObjTypeData     - expanded type information for the object
    // Note: returns an appropriate failure HRESULT on error
    virtual HRESULT STDMETHODCALLTYPE GetBasicObjectInfo(CORDB_ADDRESS objectAddress, OUT BOOL * pIsValidRef, OUT UINT * pObjSize, OUT UINT * pObjOffsetToVars, OUT DebuggerIPCE_ExpandedTypeData * pObjTypeData) = 0;

• Files reviewed: 3/3 changed files
• Comments generated: 0 new

[rcj1]

/ba-g everything is green except "build monitor helix jobs"