### 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 C.ERROR_ON_MISSING_HANDLER:
                                        raise AnsibleError(msg)
                                    else:
                                        display.warning(msg)
                    if 'add_host' in result_item:
                        
                        new_host_info = result_item.get('add_host', dict())
                        self._add_host(new_host_info, result_item)
                        post_process_whens(result_item, original_task, handler_templar)
                    elif 'add_group' in result_item:
                        
                        self._add_group(original_host, result_item)
                        post_process_whens(result_item, original_task, handler_templar)
                    if 'ansible_facts' in result_item and original_task.action not in C._ACTION_DEBUG:
                        
                        if original_task.delegate_to is not None and original_task.delegate_facts:
                            host_list = self.get_delegated_hosts(result_item, original_task)
                        else:
                            
                            self._set_always_delegated_facts(result_item, original_task)
                            host_list = self.get_task_hosts(iterator, original_host, original_task)
                        if original_task.action in C._ACTION_INCLUDE_VARS:
                            for (var_name, var_value) in iteritems(result_item['ansible_facts']):
                                
                                
                                for target_host in host_list:
                                    self._variable_manager.set_host_variable(target_host, var_name, var_value)
                        else:
                            cacheable = result_item.pop('_ansible_facts_cacheable', False)
                            for target_host in host_list: