GCRoot: Report GCFrame and in-flight exception objects

[leculver]

Threads' GCFrame objects were not being reported correctly as GCRoots. Similarly, an in-flight exception was also not being reported, though it typically has other roots it's just good to fix the gap.

This is my first real cdac change, so detailed feedback and nitpicks are very appreciated.

[Copilot]

Pull request overview

This PR extends cDAC stack reference enumeration to also report two additional GC root sources that were previously missed: (1) objects protected by the thread’s GCFrame (GCPROTECT) chain and (2) in-flight exception objects held on the thread’s ExInfo chain. It also adds new dump debuggees and dump tests to validate these root sources show up in IStackWalk.WalkStackReferences.

Changes:

• Add cDAC data contract support for GCFrame and expose the thread’s m_pGCFrame chain via the Thread contract.
• Extend StackWalk_1.WalkStackReferences to report GCFrame roots and ExInfo (exception tracker) roots.
• Add two new dump debuggees and corresponding dump tests covering GCFrame roots and nested in-flight exceptions.

Show a summary per file

File	Description
src/native/managed/cdac/tests/DumpTests/StackReferenceDumpTests.cs	Adds new dump-based tests for ExInfo and GCFrame root reporting; GCFrame test needs to avoid potential false positives.
src/native/managed/cdac/tests/DumpTests/Debuggees/NestedException/Program.cs	New debuggee that crashes while nested exceptions are still in flight.
src/native/managed/cdac/tests/DumpTests/Debuggees/NestedException/NestedException.csproj	Registers the NestedException debuggee and requests Full dumps.
src/native/managed/cdac/tests/DumpTests/Debuggees/GCProtect/Program.cs	New debuggee that FailFasts inside an AssemblyResolve handler under a native GCPROTECT scope.
src/native/managed/cdac/tests/DumpTests/Debuggees/GCProtect/GCProtect.csproj	Registers the GCProtect debuggee and requests Full dumps.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/DataType.cs	Adds GCFrame to the public DataType enum (new public surface).
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Thread.cs	Adds an optional GCFrame pointer field to the managed Thread data contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/GCFrame.cs	New managed data contract type describing the native GCFrame layout.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/StackWalk_1.cs	Reports GCFrame-protected roots and ExInfo-tracked exception roots as stack references.
src/coreclr/vm/threads.h	Exposes Thread::m_pGCFrame offset via cdac_data<Thread>.
src/coreclr/vm/frames.h	Adds cdac_data<GCFrame> describing the native GCFrame layout.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Adds Thread.GCFrame field and a new GCFrame CDAC type descriptor.

Copilot's findings

• Files reviewed: 12/12 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 12/12 changed files
• Comments generated: 5

[Copilot]

Copilot's findings

• Files reviewed: 15/15 changed files
• Comments generated: 2

[noahfalk]

Hey Lee, this looks good! Probably my only major comment is whether we should do some contract level refactoring but curious to get a 2nd opinion from Max.

[Copilot]

Copilot's findings

• Files reviewed: 22/22 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 22/22 changed files
• Comments generated: 6

[Copilot]

Copilot's findings

• Files reviewed: 22/22 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 30/30 changed files
• Comments generated: 6

[leculver]

/ba-g Helix timeouts, I can't get those to complete. Also the osx tests are actually fixed by #129462 and unrelated to my changes.