[cDAC] Implement DacDbi GetStackWalkCurrentFrameInfo

[rcj1]

• Add some more well known methodtables and method descs to the well known set on RuntimeTypeSystem
• Add IsVarArg on RuntimeTypeSystem
• Add

StackWalkFrameInfo GetCurrentFrameInfo(IStackDataFrameHandle stackDataFrameHandle) => throw new NotImplementedException();
   TargetPointer GetExactGenericArgsToken(IStackDataFrameHandle stackDataFrameHandle) => throw new NotImplementedException();

and supporting APIs on GC info contract
Implement GetStackWalkCurrentFrameInfo DacDbi API

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[Copilot]

Pull request overview

This PR extends the cDAC stack-walking and runtime type system contracts to support richer per-frame debugger data (frame classification, funclet/interrupt state, ambient SP, exact generic args token) and wires that through the legacy DacDbi implementation for GetStackWalkCurrentFrameInfo.

Changes:

• Implements DacDbiImpl.GetStackWalkCurrentFrameInfo using new StackWalk/GCInfo contract APIs and expands frame classification logic (managed EH helpers, runtime entry point, native runtime-unwindable markers).
• Extends cDAC contracts/abstractions: async method flags API, varargs detection, well-known MethodTables/MethodDescs, StackWalkFrameInfo, and GCInfo helpers (ambient SP + generic instantiation context slot).
• Updates unit tests and contract docs to reflect the new async flags behavior and new StackWalk/RuntimeTypeSystem/GCInfo surface.

Show a summary per file

File	Description
src/native/managed/cdac/tests/UnitTests/MethodDescTests.cs	Updates async-thunk classification test coverage to validate the new GetAsyncMethodFlags semantics (variant/return-dropping flags).
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/IDacDbiInterface.cs	Adds missing legacy enums/constants needed by the new frame-info shaping (FrameType, MAX_ILNUM, mapping result).
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs	Implements GetStackWalkCurrentFrameInfo and integrates new async flag checks + vararg + exact generic args token + ambient SP plumbing.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/StackWalk_1.ExceptionHandling.cs	Adds secondary-walk logic to locate funclet parent method frame info.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/StackWalk_1.cs	Extends stackwalk handle state (interrupt/fault), and implements GetCurrentFrameInfo + GetExactGenericArgsToken and helpers.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs	Adds well-known MT/MD globals accessors, exposes raw async flags, and implements IsVarArg.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/IGCInfoDecoder.cs	Extends decoder interface with generic-inst-context slot discovery + ambient SP query.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/X86/GCInfo.cs	Implements ambient SP computation for x86 GC info and reports no generic-inst-context slot for the x86 format.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/GCInfoX86_1.cs	Plumbs new ambient SP / generic-inst-context APIs through the x86 GCInfo contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/GCInfoDecoder.cs	Implements generic-inst-context stack-slot discovery for the non-x86 decoder; ambient SP returns null for non-x86.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/GCInfo_1.cs	Plumbs new APIs through the general GCInfo contract surface.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Constants.cs	Adds new global names for the additional well-known MT/MD pointers.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IStackWalk.cs	Adds StackWalkFrameInfo and new StackWalk APIs needed by DacDbi frame info shaping.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeTypeSystem.cs	Adds async flag enum/API, new well-known method desc API, and IsVarArg.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IGCInfo.cs	Adds ambient SP and generic-inst-context slot APIs.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Exposes additional well-known MT/MD globals to cDAC.
src/coreclr/inc/gcinfotypes.h	Annotates INVALID_SYNC_OFFSET as a cDAC contract dependency.
src/coreclr/inc/eetwain.h	Annotates SHADOW_SP_BITS as a cDAC contract dependency.
docs/design/datacontracts/StackWalk.md	Documents new StackWalk APIs and frame-info semantics.
docs/design/datacontracts/RuntimeTypeSystem.md	Documents new well-known MT/MD and async-flag/vararg APIs.
docs/design/datacontracts/GCInfo.md	Documents new GCInfo APIs and the constants they depend on.

Copilot's findings

Comments suppressed due to low confidence (3)

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs:1698

• GetStackWalkCurrentFrameInfo only writes *pRetVal at the end of the try block. If any exception is thrown before that point, the out-pointer remains uninitialized, which can lead to reading undefined data on the caller side even though an HRESULT failure is returned.

                hr = HResults.S_FALSE;
            }
        }
        catch (System.Exception ex)
        {

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs:5738

• Avoid Enum.HasFlag here to prevent boxing on a potentially hot path (async locals enumeration).

            Contracts.ModuleHandle handle = loader.GetModuleHandleFromModulePtr(new TargetPointer(pModule));

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs:1833

• ClassifyManagedFrame calls GetWellKnownMethodTable/GetWellKnownMethodDesc repeatedly. Each call can trigger target reads; caching these values once per classification reduces repeated reads and also avoids accidentally matching TargetPointer.Null if any well-known global isn't initialized.

        catch (System.Exception ex)
        {
            hr = ex.HResult;
        }
#if DEBUG
        if (_legacy is not null)

• Files reviewed: 21/21 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 21/21 changed files
• Comments generated: 6

[Copilot]

Copilot's findings

• Files reviewed: 21/21 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 21/21 changed files
• Comments generated: 5

[Copilot]

Copilot's findings

• Files reviewed: 21/21 changed files
• Comments generated: 5

[Copilot]

Copilot's findings

• Files reviewed: 21/21 changed files
• Comments generated: 3