### 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.
host_name = result.get('_ansible_delegated_vars', {}).get('ansible_delegated_host', None)
        return [host_name or task.delegate_to]
    def _set_always_delegated_facts(self, result, task):
        """Sets host facts for ``delegate_to`` hosts for facts that should
        always be delegated
        This operation mutates ``result`` to remove the always delegated facts
        See ``ALWAYS_DELEGATE_FACT_PREFIXES``
        """
        if task.delegate_to is None:
            return
        facts = result['ansible_facts']
        always_keys = set()
        _add = always_keys.add
        for fact_key in facts:
            for always_key in ALWAYS_DELEGATE_FACT_PREFIXES:
                if fact_key.startswith(always_key):
                    _add(fact_key)
        if always_keys:
            _pop = facts.pop
            always_facts = {
                'ansible_facts': dict((k, _pop(k)) for k in list(facts) if k in always_keys)
            }
            host_list = self.get_delegated_hosts(result, task)
            _set_host_facts = self._variable_manager.set_host_facts
            for target_host in host_list:
                _set_host_facts(target_host, always_facts)
    def normalize_task_result(self, task_result):