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/util/plugin.lua

@@ -71,31 +71,6 @@ function M.extra_idx(name)
 end
 
 function M.lazy_file()
-  -- This autocmd will only trigger when a file was loaded from the cmdline.
-  -- It will render the file as quickly as possible.
-  vim.api.nvim_create_autocmd("BufReadPost", {
-    once = true,
-    callback = function(event)
-      -- Skip if we already entered vim
-      if vim.v.vim_did_enter == 1 then
-        return
-      end
-
-      -- Try to guess the filetype (may change later on during Neovim startup)
-      local ft = vim.filetype.match({ buf = event.buf })
-      if ft then
-        -- Add treesitter highlights and fallback to syntax
-        local lang = vim.treesitter.language.get_lang(ft)
-        if not (lang and pcall(vim.treesitter.start, event.buf, lang)) then
-          vim.bo[event.buf].syntax = ft
-        end
-
-        -- Trigger early redraw
-        vim.cmd([[redraw]])
-      end
-    end,
-  })
-
   -- Add support for the LazyFile event
   local Event = require("lazy.core.handler.event")