Fix stale lastThrownObjectHandle in DAC GetThreadData during active exception dispatch

[hoyosjs]

After #127300 removed ExInfo::m_hThrowable and SetThrowable(), Thread::m_LastThrownObjectHandle is no longer updated during active exception dispatch. This causes a staleclastThrownObjectHandle to ge returned by GetThreadData when a debugger breaks into the target mid-dispatch.

When debugging a .NET 11 process with SOS (e.g. via dotnet-dump or WinDbg), the following commands fail if the debuggee is stopped during exception dispatch (for example, with SXE CLR):

• !PrintException — reports "Invalid exception object" because it dereferences the stale handle and gets a null or recycled pointer
• !Threads — shows no exception column for threads that are actively throwing
• !clrstack -a with exception context — may show incomplete or missing exception info

[hoyosjs]

@jkotas @max-charlamb - This was a regression when trying to update the last set of runtime changes in SOS tests

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[Copilot]

Pull request overview

This PR fixes debugger-visible exception reporting when the target is stopped mid-exception-dispatch by preferring the active exception stored in the ExInfo tracker (via a pseudo-handle to the exception slot) instead of relying on Thread::m_LastThrownObjectHandle, which can be stale during active dispatch after #127300.

Changes:

• Update native DAC ClrDataAccess::GetThreadData to return the active exception pseudo-handle when available, falling back to m_LastThrownObjectHandle.
• Update the cDAC thread contract to compute ThreadData.LastThrownObjectHandle from the active ExceptionInfo.ThrownObject slot when present (same pseudo-handle semantics), with fallback.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/Thread_1.cs	Prefer ExInfo-derived pseudo-handle for ThreadData.LastThrownObjectHandle; factor pseudo-handle computation into a helper used by both GetThreadData and GetCurrentExceptionHandle.
src/coreclr/debug/daccess/request.cpp	Prefer Thread::GetThrowableAsPseudoHandle() for DacpThreadData::lastThrownObjectHandle in GetThreadData, falling back to m_LastThrownObjectHandle.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

[hoyosjs]

/ba-g cDAC issue is #127774 and other legs don't get touched by this PR for anything other than builds, so timeouts are unrelated