### 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 task:
            if task._role:
                all_vars = _combine_and_track(all_vars, task._role.get_role_params(task.get_dep_chain()), "role '%s' params" % task._role.name)
            
            
            
            all_vars = _combine_and_track(all_vars, task.get_include_params(), "include params")
        
        all_vars = _combine_and_track(all_vars, self._extra_vars, "extra vars")
        
        all_vars = _combine_and_track(all_vars, magic_variables, "magic vars")
        
        
        if task:
            all_vars['environment'] = task.environment
        
        if task or play:
            
            all_vars['vars'] = all_vars.copy()
        
        
        if task and task.delegate_to is not None and include_delegate_to:
            all_vars['ansible_delegated_vars'], all_vars['_ansible_loop_cache'] = self._get_delegated_vars(play, task, all_vars)
        display.debug("done with get_vars()")
        if C.DEFAULT_DEBUG:
            
            return VarsWithSources.new_vars_with_sources(all_vars, _vars_sources)
        else:
            return all_vars
    def _get_magic_variables(self, play, host, task, include_hostvars, include_delegate_to,