fix(ext/node): count forked child process sockets

[bartlomieju]

Summary

• add fork IPC socket-list accounting for sockets transferred to child processes
• include child-owned transferred sockets in net.Server#getConnections()
• enable test-child-process-fork-getconnections.js in node compat config on non-Windows platforms

Tests

• ./x build
• ./x test-compat test-child-process-fork-getconnections.js
• ./x test-compat test-child-process-send-keep-open.js test-child-process-fork-net-socket.js test-child-process-fork-net.js