[BUG] pillar.file_exists doesn't test directories, and there's no pillar.directory_exists

Description
calling
{% if salt['pillar.file_exists']('test') %}
always fails. Just changing it to
{% if salt['pillar.file_exists']('test/init.sls') %}
works as expected (as long as test/init.sls is there, even if empty).

Setup
From /srv/pillar:

• top.sls (working version):

{% set dom=grains['domain']|replace('.', '_') %}
{% set hostbase = "{0}_{1}".format(grains['host'], dom) %}
base:
  '*':
    - default
{% if salt['pillar.file_exists']('hostdata/'+hostbase+'.sls') %}
    - hostdata.{{hostbase}}
{% endif %}

{% if salt['pillar.file_exists'](dom+'/init.sls') %}
  '*.{{ grains['domain'] }}':
    - {{ dom }} # init.sls contains the domain defaults
{% if salt['pillar.file_exists']("{0}/{1}".format(dom,grains['host'])+'.sls') %}
    - {{ dom }}.{{ grains['host'] }} # Host-specific pillars
{% endif %}
{% endif %}

• hostdata/host_domain_name_tld.sls : generic pillar data for host
• domain_name_tld/ : pillar data for hosts in domain.name.tld
• domain_name_tld/host.sls : pillar data for host.domain.name.tld

• on-prem machine
• VM (Virtualbox, KVM, etc. please specify) kvm
• VM running on a cloud service, please be explicit and add details
• container (Kubernetes, Docker, containerd, etc. please specify)
• or a combination, please be explicit
• jails if it is FreeBSD

Steps to Reproduce the behavior
salt '*' saltutil.refresh_pillar && salt ctl\* pillar.items
does not show items in domain_name_tld/host.sls since the first if fails when testing the directory. If, like in the snippet above, I test for init.sls, it works as expected.

Expected behavior
pillar.file_exists should treat a directory like a file and return true if it exists. Alternatively, there should be a pillar.directory_exists function (and a notice in the docs, maybe).

Versions Report

Salt Version:
          Salt: 3004.1
 
Dependency Versions:
          cffi: Not Installed
      cherrypy: Not Installed
      dateutil: 2.8.1
     docker-py: Not Installed
         gitdb: 4.0.5
     gitpython: 3.1.14
        Jinja2: 2.11.3
       libgit2: 1.1.0
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 1.0.0
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     pycparser: Not Installed
      pycrypto: Not Installed
  pycryptodome: 3.9.7
        pygit2: 1.4.0
        Python: 3.9.2 (default, Feb 28 2021, 17:03:44)
  python-gnupg: Not Installed
        PyYAML: 5.3.1
         PyZMQ: 20.0.0
         smmap: 4.0.0
       timelib: Not Installed
       Tornado: 4.5.3
           ZMQ: 4.3.4
 
System Versions:
          dist: debian 11 bullseye
        locale: utf-8
       machine: x86_64
       release: 5.10.0-14-amd64
        system: Linux
       version: Debian GNU/Linux 11 bullseye

Start at the pillar.file_exists entry point and reproduce the reported behavior using the provided top.sls layout, checking both an existing directory and a file path. Determine whether the expected behavior is directory recognition or a separate directory_exists API; done means the selected behavior works for the pillar layout and is documented or covered by verification.