[BUG] systemd templated services not handled correctly

Description
Under systemd you can have multiple services based on the same unit file. These will be listed containing an @ in the service name. Some Salt functions, e.g. systemd_service.get_all do not handle this correctly.

Setup
Be logged in to any systemd system.

Steps to Reproduce the behavior

# salt-call --local service.get_all | grep '@'
    - autovt@
    - blockdev@.target
    - container-getty@
    - e2scrub@
    - e2scrub_fail@
    - getty@
    - lvm2-pvscan@
    - modprobe@
    - postgresql@
    - salt-proxy@
    - serial-getty@
    - ssh@
    - systemd-backlight@
    - systemd-fsck@
    - systemd-hibernate-resume@
    - systemd-journald-varlink@.socket
    - systemd-journald@
    - systemd-journald@.socket
    - user-runtime-dir@
    - user@

# systemctl list-units --plain --all --type=service '*@*'
  UNIT                                        LOAD   ACTIVE   SUB     DESCRIPTION
  getty@tty1.service                          loaded active   running Getty on tty1
  lvm2-pvscan@252:1.service                   loaded active   exited  LVM event activation on device 252:1
  modprobe@drm.service                        loaded inactive dead    Load Kernel Module drm
  postgresql@12-main.service                  loaded active   running PostgreSQL Cluster 12-main
  systemd-fsck@dev-mapper-vg1\x2ddata.service loaded active   exited  File System Check on /dev/mapper/vg1-data
  systemd-fsck@dev-mapper-vg1\x2dvar.service  loaded active   exited  File System Check on /dev/mapper/vg1-var
  user-runtime-dir@112.service                loaded active   exited  User Runtime Directory /run/user/112
  user-runtime-dir@216216.service             loaded active   exited  User Runtime Directory /run/user/216216
  user@112.service                            loaded active   running User Manager for UID 112
  user@216216.service                         loaded active   running User Manager for UID 216216

Expected behavior
Should include the full names of each service, including multiple for the same template.

Versions Report

Salt Version:
          Salt: 3003

Dependency Versions:
          cffi: 1.14.5
      cherrypy: Not Installed
      dateutil: 2.7.3
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 2.10.1
       libgit2: 1.1.0
      M2Crypto: 0.31.0
          Mako: Not Installed
       msgpack: 0.6.2
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     pycparser: 2.20
      pycrypto: Not Installed
  pycryptodome: 3.6.1
        pygit2: 1.5.0
        Python: 3.8.5 (default, Jan 27 2021, 15:41:15)
  python-gnupg: 0.4.5
        PyYAML: 5.3.1
         PyZMQ: 18.1.1
         smmap: Not Installed
       timelib: Not Installed
       Tornado: 4.5.3
           ZMQ: 4.3.2

System Versions:
          dist: ubuntu 20.04 focal
        locale: utf-8
       machine: x86_64
       release: 5.4.0-71-generic
        system: Linux
       version: Ubuntu 20.04 focal

Additional context
systemctl list-units can't show services from unloaded units, e.g. salt-proxy. In an attempt to represent "disabled" services, salt is probably conflating units with unit files.

Start with the systemd_service.get_all and service.get_all entry points, then reproduce the behavior using salt-call --local service.get_all and the listed systemctl command on a systemd host. Done means the service listing preserves full templated service names, includes multiple instances of the same template, and does not conflate unit files with loaded units.