### 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 delegated_host is None:
                    for h in self._inventory.get_hosts(ignore_limits=True, ignore_restrictions=True):
                        
                        
                        if h.address == delegated_host_name:
                            delegated_host = h
                            break
                    else:
                        delegated_host = Host(name=delegated_host_name)
            else:
                delegated_host = Host(name=delegated_host_name)
            
            
            delegated_host_vars[delegated_host_name] = self.get_vars(
                play=play,
                host=delegated_host,
                task=task,
                include_delegate_to=False,
                include_hostvars=True,
            )
            delegated_host_vars[delegated_host_name]['inventory_hostname'] = vars_copy.get('inventory_hostname')
        _ansible_loop_cache = None
        if has_loop and cache_items:
            
            
            
            
            _ansible_loop_cache = items
        return delegated_host_vars, _ansible_loop_cache
    def clear_facts(self, hostname):