### 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.
_ALLOWED = frozenset(['plugins_by_group', 'groups_plugins_play', 'groups_plugins_inventory', 'groups_inventory',
                          'all_plugins_play', 'all_plugins_inventory', 'all_inventory'])
    def __init__(self, loader=None, inventory=None, version_info=None):
        self._nonpersistent_fact_cache = defaultdict(dict)
        self._vars_cache = defaultdict(dict)
        self._extra_vars = defaultdict(dict)
        self._host_vars_files = defaultdict(dict)
        self._group_vars_files = defaultdict(dict)
        self._inventory = inventory
        self._loader = loader
        self._hostvars = None
        self._omit_token = '__omit_place_holder__%s' % sha1(os.urandom(64)).hexdigest()
        self._options_vars = load_options_vars(version_info)
        
        
        basedir = self._options_vars.get('basedir', False)
        self.safe_basedir = bool(basedir is False or basedir)
        
        self._extra_vars = load_extra_vars(loader=self._loader)
        
        try:
            self._fact_cache = FactCache()
        except AnsibleError as e:
            
            
            display.warning(to_text(e))
            self._fact_cache = {}
    def __getstate__(self):