Add InterlockedExchangeAdd to kernel32 API stubs

[dinis-cruz-bs]

InterlockedExchangeAdd is a commonly used kernel32 export for atomic
addition (CRT, COM, and many third-party runtimes call it). Without a stub,
emulation hits an unsupported_api error during DLL_PROCESS_ATTACH and
terminates before any subsequent API calls can be captured.

Implementation reads the current DWORD at Addend, adds Value, writes
the result back, and returns the original value — matching the documented
Windows behaviour.

Placed alongside the existing InterlockedIncrement /
InterlockedDecrement stubs in kernel32.py.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[gemini-code-assist]

Code Review

This pull request implements the InterlockedExchangeAdd API hook in kernel32.py, which performs an atomic addition to a memory address and returns the original value. The feedback suggests explicitly masking the input value to 32 bits before the addition to ensure the operation remains consistent, particularly in 64-bit environments where registers might contain extraneous data in the upper bits.

[williballenthin]

thanks @dinis-cruz-bs!