### 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 attribute.static:
                value = getattr(self, name)
                
                if name not in ('vars',) and templar.is_template(value):
                    display.warning('"%s" is not templatable, but we found: %s, '
                                    'it will not be templated and will be used "as is".' % (name, value))
                continue
            if getattr(self, name) is None:
                if not attribute.required:
                    continue
                else:
                    raise AnsibleParserError("the field '%s' is required but was not set" % name)
            elif not attribute.always_post_validate and self.__class__.__name__ not in ('Task', 'Handler', 'PlayContext'):
                
                
                
                continue
            try:
                
                
                method = getattr(self, '_post_validate_%s' % name, None)
                if method:
                    value = method(attribute, getattr(self, name), templar)
                elif attribute.isa == 'class':
                    value = getattr(self, name)
                else:
                    
                    value = templar.template(getattr(self, name))