### 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.
is_set_fact = original_task.action in C._ACTION_SET_FACT
                                if not is_set_fact or cacheable:
                                    self._variable_manager.set_host_facts(target_host, result_item['ansible_facts'].copy())
                                if is_set_fact:
                                    self._variable_manager.set_nonpersistent_facts(target_host, result_item['ansible_facts'].copy())
                    if 'ansible_stats' in result_item and 'data' in result_item['ansible_stats'] and result_item['ansible_stats']['data']:
                        if 'per_host' not in result_item['ansible_stats'] or result_item['ansible_stats']['per_host']:
                            host_list = self.get_task_hosts(iterator, original_host, original_task)
                        else:
                            host_list = [None]
                        data = result_item['ansible_stats']['data']
                        aggregate = 'aggregate' in result_item['ansible_stats'] and result_item['ansible_stats']['aggregate']
                        for myhost in host_list:
                            for k in data.keys():
                                if aggregate:
                                    self._tqm._stats.update_custom_stats(k, data[k], myhost)
                                else:
                                    self._tqm._stats.set_custom_stats(k, data[k], myhost)
                if 'diff' in task_result._result:
                    if self._diff or getattr(original_task, 'diff', False):
                        self._tqm.send_callback('v2_on_file_diff', task_result)
                if not isinstance(original_task, TaskInclude):
                    self._tqm._stats.increment('ok', original_host.name)
                    if 'changed' in task_result._result and task_result._result['changed']:
                        self._tqm._stats.increment('changed', original_host.name)