[lldb][Windows] Support OutputDebugString (#196395)
This picks https://reviews.llvm.org/D128541 back up. It implements
support for `OutputDebugStringA/W` on Windows. It's used by some logging
systems.
The main changes since the original patch:
- Use `WaitForDebugEventEx` for getting debug events over
`WaitForDebugEvent`. According to the
[docs](https://learn.microsoft.com/en-us/windows/win32/api/debugapi/nf-debugapi-waitfordebugeventex),
the only difference is that the -Ex version correctly outputs Unicode
strings.
- Support strings longer than 64 KiB. I set an arbitrary limit of 1 MiB
for the strings we read. The debugger interface only tells us the length
modulo 64 KiB which is a bit awkward. Libraries like Qt already chunk
calls to `OutputDebugString`, so strings shouldn't be too big in
practice.
- Output to stdout instead of a log channel, so the output is always
enabled. I don't know if this should go to stdout or stderr.
Tested that it works with lldb-dap and shows up in the debug console in
all modes.
Closes #185891.
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Co-authored-by: Alvin Wong <alvin@alvinhc.com>
