Can anyone provide some guidance on how to load a vim plugin installed with packer in Neovim?

Up till now, I've only ever used plugins written in Lua in Nvim but, I'm trying to install vim-expand-region which is written in Vim Script.

I added use { "terryma/vim-expand-region" } to my plugins.lua file and it was installed with Packer. At least, there is a vim-expand-region directory in ~/.local/share/nvim/site/pack/packer/start.

My current config is organized like this:

~/.config/nvim/
├── init.lua
├── lua
│   └── user
│       ├── alpha.lua
│       ├── autocommands.lua
│       ├── autopairs.lua
│       ├── bufferline.lua
│       ├── cmp.lua
│       ├── colorscheme.lua
│       ├── comment.lua
│       ├── dap
│       │   ├── dap.lua
│       │   ├── dap-python.lua
│       │   ├── init.lua
│       │   └── osv.lua
│       ├── gitsigns.lua
│       ├── hop.lua
│       ├── icons.lua
│       ├── illuminate.lua
│       ├── impatient.lua
│       ├── indentline.lua
│       ├── keymaps.lua
│       ├── lsp
│       │   ├── handlers.lua
│       │   ├── init.lua
│       │   ├── mason.lua
│       │   ├── null-ls.lua
│       │   ├── package-lock.json
│       │   └── settings
│       │       ├── pyright.lua
│       │       └── sumneko_lua.lua
│       ├── lualine.lua
│       ├── navic.lua
│       ├── neoclip.lua
│       ├── nvim-surround.lua
│       ├── nvim-tree.lua
│       ├── options.lua
│       ├── plugins.lua
│       ├── symbols-outline.lua
│       ├── tabnine.lua
│       ├── telescope.lua
│       ├── toggleterm.lua
│       ├── treesitter.lua
│       ├── vim-expand-region.lua
│       └── whichkey.lua
└── plugin
    └── packer_compiled.lua

As described in the nanotee guide, to load a .lua plugin, I run require "user.plugin" in my init.lua file. Then, in the plugin.lua file, I require the plugin itself with code like:

local status_ok, plugin = pcall(require, "plugin")
if not status_ok then
    vim.notify("WARNING: plugin.lua failed to load.")
    return
end

As I understand it, the require function searches the runtime path looking for a file called "plugin.lua" to load. In my case, my runtime path includes ~/.local/share/nvim/site/pack/*/start/* and each of the lua plugins installed with Packer contains a lua directory with a plugin.lua file (e.g. ~/.local/share/nvim/site/pack/*/start/plugin/lua/plugin.lua) which I assume gets sourced when the require function is called.

However, the vim plugin vim-expand-region has this structure:

~/.local/share/nvim/site/pack/packer/start/vim-expand-region/
├── autoload
│   └── expand_region.vim
├── doc
│   ├── expand_region.txt
│   └── tags
├── expand-region.gif
├── MIT-LICENSE.txt
├── plugin
│   └── expand_region.vim
└── README.md

Vim configs that use the Plug package manager load the plugin with a line like Plug 'terryma/vim-expand-region' but since I'm not using Plug, I'm not sure how I should load it.

From some of the instructions listed here it seems like the expand_region.vim file needs to be sourced. For vim it seems like the plugin should be added to ~/.vim/pack/bundle/start but that's not where it gets installed with Packer.

What is the best way to load vim plugins that have been installed with Packer?