lsp: Push sphinx output through the logging system

This ensures that sphinx output obeys settings like `esbonio.logging.window`

lib/esbonio/esbonio/server/features/sphinx_manager/client_subprocess.py

@@ -273,8 +273,7 @@ async def forward_stderr(server: asyncio.subprocess.Process):
 
     # EOF is signalled with an empty bytestring
     while (line := await server.stderr.readline()) != b"":
-        sys.stderr.buffer.write(line)
-        sys.stderr.buffer.flush()
+        sphinx_logger.info(line.decode())
 
 
 def make_subprocess_sphinx_client(