vpx: watch reports for vpx --watch, and vpx watch on oxc-node's watcher #3141

Follow-up to #2936. vpx --watch is Node.js watch mode with the script loader. It restarts when an imported file changes, but not in two common cases, which tsx watch misses as well:

• A tsconfig edit, such as a new paths mapping.
• A file an import is waiting for, created after the first run (import "./later.js", then later.ts is added).

It also has none of tsx watch's options: include and exclude globs, clearing the screen, rerunning on Enter, a kill timeout, or polling for Docker, WSL, and network drives.

oxc-node added both pieces in oxc-project/oxc-node#861, which #2936 syncs (ce22828):

1. Dependency reports. With enable_watch_report on, the binding records the tsconfig files it reads and the paths a failed resolve looked for. @oxc-node/core's loader sends them as { "watch:import": [url] } over IPC, the message Node.js's own watcher already reads, so node --watch restarts on them.
2. oxnode watch. A tsx-style watcher, about 2,500 lines of TypeScript on Node.js built-ins.

Plan

1. Reports for vpx --watch. Forward enable_watch_report and take_watch_dependencies in packages/cli/binding/src/oxc_node.rs. Port the relay into vpx's loader: the preload reports on the in-thread path, and the off-thread hooks send through a channel to the main thread. It is on only when WATCH_REPORT_DEPENDENCIES is set. vpx --watch then restarts on tsconfig edits and created files, with no new process.
2. Signal ack. Port the child's side of OXNODE_SIGNAL_ACK into the preload, so the watcher does not deliver Ctrl+C twice when it runs in a pipe or the background.
3. vpx watch. Run oxc-node's watcher, bundled from the vendored source, once Expose the oxnode watch watcher as an entry an embedder can run with its own loader oxc-project/oxc-node#871 gives it an entry that takes vpx's loader and name.
   • Both CLIs route vpx watch <script>: the global vpx execs Node.js with the bundled watcher, and the local bin calls it in process.
   • Add docs and snapshots, and a vp migrate rule that rewrites tsx watch to vpx watch.

Notes

• vpx watch currently runs the binary of the npm package watch. A subcommand changes that, as tsx and oxnode did.
• The process count matches vpx --watch, since Node.js watch mode also runs a watcher process above the script.
• Step 1 does not depend on Expose the oxnode watch watcher as an entry an embedder can run with its own loader oxc-project/oxc-node#871 and can land first.