fix: incorrect parsing of closeFDs option

[deepak1556]

Refs microsoft/vscode-remote-release#7964

When running strace on the scenarios mentioned in the above issue, the spawn helper was spending a lot of time on closing the inherited file descriptors

node-pty/src/unix/spawn-helper.cc

Lines 58 to 64 in 42b5ce4

	struct rlimit rlim_ofile;
	getrlimit(RLIMIT_NOFILE, &rlim_ofile);
	for (rlim_t fd = STDERR_FILENO + 1; fd < rlim_ofile.rlim_cur; fd++) {
	if (fd != COMM_PIPE_FD) {
	close(fd);
	}
	}

VSCode does not use the closeFDs option but it was being enabled because of incorrect positional parsing and this PR addresses that.

Additionally, if VSCode were to use closeFDs option we will hit the above issue as in most cases the soft limit of file handles can easily be in the 100k range. A better approach would be to first check if /proc/pid/fd is available in the child process and only restrict to closing the descriptors from this location, fallback can be to loop on the rlimit. I will address this in a follow-up PR.