### 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.
raise AnsibleError('Unknown playbook vars logic: %s' % C.PLAYBOOK_VARS_ROOT)
            
            
            
            if task._role is not None and (play or task.action in C._ACTION_INCLUDE_ROLE):
                all_vars = _combine_and_track(all_vars, task._role.get_default_vars(dep_chain=task.get_dep_chain()),
                                              "role '%s' defaults" % task._role.name)
        if host:
            
            all_group = self._inventory.groups.get('all')
            host_groups = sort_groups([g for g in host.get_groups() if g.name not in ['all']])
            def _get_plugin_vars(plugin, path, entities):
                data = {}
                try:
                    data = plugin.get_vars(self._loader, path, entities)
                except AttributeError:
                    try:
                        for entity in entities:
                            if isinstance(entity, Host):
                                data.update(plugin.get_host_vars(entity.name))
                            else:
                                data.update(plugin.get_group_vars(entity.name))
                    except AttributeError:
                        if hasattr(plugin, 'run'):
                            raise AnsibleError("Cannot use v1 type vars plugin %s from %s" % (plugin._load_name, plugin._original_path))
                        else:
                            raise AnsibleError("Invalid vars plugin %s from %s" % (plugin._load_name, plugin._original_path))
                return data
            
            def _plugins_inventory(entities):