child_process: stdout support stream

[Tseian]

Issue

#52776

Description

Enable child_process.spawnSync() to accept wrapped libuv streams (stdio.wrap) as stdio targets (e.g. passing another child process’ stdin), so synchronous spawns can participate in stream wiring the same way spawn() does.

This makes it possible to forward a spawnSync() child’s output directly into an existing stream without creating intermediate pipes.

Before

Passing an existing stream as a spawnSync() stdio entry (the stdio.wrap path) would fail (e.g. rejected as invalid / not handled), preventing patterns like wiring spawnSync() output into another child process’ stdin.

After

spawnSync() supports stdio.wrap by inheriting the provided uv_stream_t for the requested fd, allowing spawnSync() output to be forwarded into an existing stream.

Changes

• src/spawn_sync.cc
• src/spawn_sync.h
• test/parallel/test-child-process-spawnsync.js

Test

• test/parallel/test-child-process-spawnsync.js
  • Adds coverage for using another child process stream as a spawnSync() stdio target and verifies data is forwarded correctly.