Use explicit ANSI Win32 APIs for Windows IPC

[aycph]

Fixes #1116.

This PR makes the Windows IPC code use explicit ANSI Win32 APIs consistently in InterProcessCommunicatorWin.cpp.

In particular, it changes DefWindowProc to DefWindowProcA in TW_HiddenWindowProc. On my affected Windows setup, this restores successful creation of the hidden IPC message window, and second-instance forwarding works normally again.

For consistency with the rest of this file, this PR also changes:

• GetModuleHandle -> GetModuleHandleA
• GetWindowLongPtr -> GetWindowLongPtrA
• SetWindowLongPtr -> SetWindowLongPtrA

[aycph]

For GetModuleHandle, since the argument here is NULL, the A/W distinction does not appear to make a practical difference at this call site. I still changed it to the A version to match the other explicit ANSI calls in this file, as the file does not use wide string literals.

If any part of this approach is not appropriate, please feel free to adjust it as you see fit.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 34.18%. Comparing base (9f55638) to head (5c3ced9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1117      +/-   ##
==========================================
- Coverage   34.46%   34.18%   -0.29%     
==========================================
  Files         153      153              
  Lines       17592    19038    +1446     
  Branches     2420     2420              
==========================================
+ Hits         6063     6508     +445     
- Misses      11529    12530    +1001     

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