### 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.
self._fact_cache = data.get('fact_cache', defaultdict(dict))
        self._nonpersistent_fact_cache = data.get('np_fact_cache', defaultdict(dict))
        self._vars_cache = data.get('vars_cache', defaultdict(dict))
        self._extra_vars = data.get('extra_vars', dict())
        self._host_vars_files = data.get('host_vars_files', defaultdict(dict))
        self._group_vars_files = data.get('group_vars_files', defaultdict(dict))
        self._omit_token = data.get('omit_token', '__omit_place_holder__%s' % sha1(os.urandom(64)).hexdigest())
        self._inventory = data.get('inventory', None)
        self._options_vars = data.get('options_vars', dict())
        self.safe_basedir = data.get('safe_basedir', False)
        self._loader = None
        self._hostvars = None
    @property
    def extra_vars(self):
        return self._extra_vars
    def set_inventory(self, inventory):
        self._inventory = inventory
    def get_vars(self, play=None, host=None, task=None, include_hostvars=True, include_delegate_to=True, use_cache=True,