### 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.
try:
        if self._squashed:
            return self._attributes[prop_name]
        method = "_get_attr_%s" % prop_name
        return getattr(self, method)()
    except KeyError:
        raise AttributeError("'%s' object has no attribute '%s'" % (self.__class__.__name__, prop_name))
def _generic_g_parent(prop_name, self):
    try:
        if self._squashed or self._finalized:
            value = self._attributes[prop_name]
        else:
            try:
                value = self._get_parent_attribute(prop_name)
            except AttributeError:
                value = self._attributes[prop_name]
    except KeyError:
        raise AttributeError("'%s' object has no attribute '%s'" % (self.__class__.__name__, prop_name))
    if value is Sentinel:
        value = self._attr_defaults[prop_name]
    return value
def _generic_s(prop_name, self, value):
    self._attributes[prop_name] = value
def _generic_d(prop_name, self):
    del self._attributes[prop_name]
class BaseMeta(type):