src: initialize file trace writer on tracing thread

Run the initialization for the file trace writer’s `uv_async_t`s
on the same thread as `uv_run()` for their loop to avoid race
conditions.

PR-URL: https://github.com/nodejs/node/pull/21867


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>