### 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.
'''
        Given a dictionary of values, load up the field attributes for
        this object. As with serialize(), if there are any non-field
        attribute data members, this method will need to be overridden
        and extended.
        '''
        if not isinstance(data, dict):
            raise AnsibleAssertionError('data (%s) should be a dict but is a %s' % (data, type(data)))
        for (name, attribute) in iteritems(self._valid_attrs):
            if name in data:
                setattr(self, name, data[name])
            else:
                if callable(attribute.default):
                    setattr(self, name, attribute.default())
                else:
                    setattr(self, name, attribute.default)
        
        setattr(self, '_uuid', data.get('uuid'))
        self._finalized = data.get('finalized', False)
        self._squashed = data.get('squashed', False)
class Base(FieldAttributeBase):
    _name = FieldAttribute(isa='string', default='', always_post_validate=True, inherit=False)