[cDAC] Move AMD64 Unwinder to managed code

[max-charlamb]

Ports the AMD64 unwinder to managed code. The cDAC uses this managed version instead of deferring to the runtime native copy.

I'm leaving the native building infra in place until the ARM64 unwinder is ported and all of the native linking can be removed.

[max-charlamb]

/azp run runtime-diagnostics

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[dotnet-policy-service]

Tagging subscribers to this area: @steveisok, @dotnet/dotnet-diag
See info in area-owners.md if you want to be subscribed.

[max-charlamb]

/azp run runtime-diagnostics

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull Request Overview

This PR transitions the AMD64 unwinding logic from a static native helper call into fully managed code using the new AMD64Unwinder class.

• Added a using for the AMD64Unwinder namespace.
• Replaced Unwinder.AMD64Unwind(ref this, target) with instantiation of AMD64Unwinder and its Unwind method.

Comments suppressed due to low confidence (1)

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/AMD64Context.cs:54

• This new managed unwinder path should be covered by unit or integration tests to ensure the behavior matches the previous native implementation under various stack scenarios.

AMD64Unwinder unwinder = new(target);

[Copilot]

Instantiating AMD64Unwinder on each call may introduce heap allocations in hot paths. If performance is critical, consider making AMD64Unwinder a struct or caching a single instance to minimize allocations.

[max-charlamb]

/azp run runtime-diagnostics

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[max-charlamb]

/ba-g test failures unrelated to cDAC change. Both runtime-diagnostics and CLR_Tools_Tests are passing.