### 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.
''' walk the input datastructure and assign any values '''
        if ds is None:
            raise AnsibleAssertionError('ds (%s) should not be None but it is.' % ds)
        
        setattr(self, '_ds', ds)
        
        
        self._variable_manager = variable_manager
        
        if loader is not None:
            self._loader = loader
        else:
            self._loader = DataLoader()
        
        
        
        ds = self.preprocess_data(ds)
        self._validate_attributes(ds)
        
        
        for name, attr in sorted(iteritems(self._valid_attrs), key=operator.itemgetter(1)):
            
            target_name = name
            if name in self._alias_attrs:
                target_name = self._alias_attrs[name]
            if name in ds:
                method = getattr(self, '_load_%s' % name, None)
                if method:
                    self._attributes[target_name] = method(name, ds[name])
                else: