### 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.
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from __future__ import (absolute_import, division, print_function)
__metaclass__ = type
import cmd
import functools
import os
import pprint
import sys
import threading
import time
from collections import deque
from multiprocessing import Lock
from jinja2.exceptions import UndefinedError
from ansible import constants as C
from ansible import context
from ansible.errors import AnsibleError, AnsibleFileNotFound, AnsibleParserError, AnsibleUndefinedVariable
from ansible.executor import action_write_locks
from ansible.executor.process.worker import WorkerProcess
from ansible.executor.task_result import TaskResult
from ansible.executor.task_queue_manager import CallbackSend
from ansible.module_utils.six.moves import queue as Queue
from ansible.module_utils.six import iteritems, itervalues, string_types
from ansible.module_utils._text import to_text
from ansible.module_utils.connection import Connection, ConnectionError
from ansible.playbook.conditional import Conditional
from ansible.playbook.handler import Handler