### Summary

Executing a playbook with many hosts, there is massive overhead in checking whether the hosts list is a pattern, see for yourself on this callgrind graph:

![grafik](https://user-images.githubusercontent.com/3154871/111359016-4a4bf480-868b-11eb-8c8f-55b6a6a10bd7.png)

https://github.com/ansible/ansible/blob/da60525610a384bb04833b1c6429d9db6a87ef64/lib/ansible/vars/manager.py#L490

That check has quadratic runtime with the number of hosts - with a lot of hosts, commenting that check out reduces runtime manyfold.

### Issue Type

Bug Report

### Component Name

variable manager

### Ansible Version

2.10.5, devel

### OS / Environment

Ubuntu

### Steps to Reproduce

```yaml
- hosts: localhost
  tasks:
    - set_fact:
        extra_tasks: true # compute it
        hosts: "{{ [an, array, with, 5100, computed, hosts] }}"

- hosts: "{{ hostvars.localhost.hosts }}"
  vars:
    extra_tasks: "{{ hostvars.localhost.do_extra_tasks }}"
  tasks:
   # some more tasks here
    - name: Execute extra tasks
      command: /bin/true # example
      when: extra_tasks
```

### Expected Results

Execute in tens of seconds.

### Actual Results

Take over 5 minutes to execute.
throttle = int(templar.template(task.throttle))
        except Exception as e:
            raise AnsibleError("Failed to convert the throttle value to an integer.", obj=task._ds, orig_exc=e)
        
        try:
            
            
            
            
            
            rewind_point = len(self._workers)
            if throttle > 0 and self.ALLOW_BASE_THROTTLING:
                if task.run_once:
                    display.debug("Ignoring 'throttle' as 'run_once' is also set for '%s'" % task.get_name())
                else:
                    if throttle <= rewind_point:
                        display.debug("task: %s, throttle: %d" % (task.get_name(), throttle))
                        rewind_point = throttle
            queued = False
            starting_worker = self._cur_worker
            while True:
                if self._cur_worker >= rewind_point:
                    self._cur_worker = 0
                worker_prc = self._workers[self._cur_worker]
                if worker_prc is None or not worker_prc.is_alive():
                    self._queued_task_cache[(host.name, task._uuid)] = {
                        'host': host,
                        'task': task,
                        'task_vars': task_vars,
                        'play_context': play_context