### 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.
if 'changed' in task_result._result and task_result._result['changed']:
                        self._tqm._stats.increment('changed', original_host.name)
                self._tqm.send_callback('v2_runner_on_failed', task_result, ignore_errors=ignore_errors)
            elif task_result.is_unreachable():
                ignore_unreachable = original_task.ignore_unreachable
                if not ignore_unreachable:
                    self._tqm._unreachable_hosts[original_host.name] = True
                    iterator._play._removed_hosts.append(original_host.name)
                else:
                    self._tqm._stats.increment('skipped', original_host.name)
                    task_result._result['skip_reason'] = 'Host %s is unreachable' % original_host.name
                self._tqm._stats.increment('dark', original_host.name)
                self._tqm.send_callback('v2_runner_on_unreachable', task_result)
            elif task_result.is_skipped():
                self._tqm._stats.increment('skipped', original_host.name)
                self._tqm.send_callback('v2_runner_on_skipped', task_result)
            else:
                role_ran = True
                if original_task.loop:
                    
                    
                    result_items = task_result._result.get('results', [])
                else:
                    result_items = [task_result._result]
                for result_item in result_items:
                    if '_ansible_notify' in result_item:
                        if task_result.is_changed():