Design cDAC level API to expose stack walking

[max-charlamb]

Proposal 1

Using opaque IStackWalkHandle and IStackFrameHandle to hold state about the stack walk. These are passed back to the contract to be operated on.

// Each Contract version implements its own opaque handle StackWalkFrameHandle_1 for IStackFrameHandle and IStackWalkHandle etc..
// These are checked when passed in to verify that it is from the write contract version, otherwise an invalid argument exception is thrown
// This allows for flexibility in the handle implementation
//  
// if (uncheckedHandle is not StackWalkHandle_1 stackWalkHandle)
// {
//     throw new InvalidArgumentException();
// }

internal interface IStackFrameHandle { }

internal interface IStackWalkHandle { }

// IStackContext is implemented by each architectures thread context object. 

internal interface IStackContext 
{
    int GetContextSize();
    int GetContextFlags();
    TargetPointer GetIP();
    TargetPointer GetSP();
    bool WriteToBuffer(Span<byte> buffer);
}

internal interface IStackWalk : IContract
{
    // Creates a StackWalk 
    public IStackWalkHandle CreateStackWalk(ThreadData threadData);

    // Moves stackWalkHandle to the next managed frame
    // returns true if successful, false otherwise
    public bool Next(IStackWalkHandle stackWalkHandle);
    public IStackFrameHandle GetFrame(IStackWalkHandle stackWalkHandle);
    public IStackFrameContext GetContext(IStackWalkHandle stackWalkHandle);
    public int GetNumArgs(IStackFrameHandle stackFrameHandle);
    // ... other functions implemented on IXCLRDataFrame
}

Proposal 2

Same as proposal 1, except that instead of passing the opaque handles back to the contract, these can be operated on themselves.

internal interface IStackFrameHandle 
{
    // frame specific methods currently implemented on IXCLRDataFrame
    public int GetNumArgs();
    //...
}

internal interface IStackWalkHandle 
{
    // Moves stackWalkHandle to the next managed frame
    // returns true if successful, false otherwise
    public bool Next(IStackWalkHandle stackWalkHandle);
    public IStackFrameContext GetContext(IStackFrameHandle stackFrameHandle);
    public IStackFrameHandle GetFrame(IStackWalkHandle stackWalkHandle);
}

internal interface IStackWalk : IContract
{
    // Creates a StackWalk 
    public IStackWalkHandle CreateStackWalk(ThreadData threadData);
}

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