feat(core)!: move a bunch of LazyVim features to snacks.nvim (#4706)

## Description

LazyVim comes with a bunch of smaller QoL plugin like features, but it's
not easy for non LazyVim users to use them.

That's why I started working on
[snacks.nvim](https://github.com/folke/snacks.nvim), a collection of
small QoL plugins for Neovim.

Snacks also includes a bunch of new improvements to these features.

This PR fully integrates with snacks.

## Todo

- [ ] add proper deprecations where needed
- [ ] create snacks docs
- [ ] document all the new improvements relevant to LazyVim users

## Closes

- [ ] #4492 
- [ ] #4333
- [ ] #4687

## Screenshots

<!-- Add screenshots of the changes if applicable. -->

## Checklist

- [ ] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/lang/markdown.lua

@@ -108,7 +108,7 @@ return {
     ft = { "markdown", "norg", "rmd", "org" },
     config = function(_, opts)
       require("render-markdown").setup(opts)
-      LazyVim.toggle.map("<leader>um", {
+      Snacks.toggle({
         name = "Render Markdown",
         get = function()
           return require("render-markdown.state").enabled
@@ -121,7 +121,7 @@ return {
             m.disable()
           end
         end,
-      })
+      }):map("<leader>um")
     end,
   },
 }