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/init.lua

@@ -10,7 +10,48 @@ end
 
 require("lazyvim.config").init()
 
+-- Terminal Mappings
+local function term_nav(dir)
+  ---@param self snacks.terminal
+  return function(self)
+    return self:is_floating() and "<c-" .. dir .. ">" or vim.schedule(function()
+      vim.cmd.wincmd(dir)
+    end)
+  end
+end
+
 return {
   { "folke/lazy.nvim", version = "*" },
   { "LazyVim/LazyVim", priority = 10000, lazy = false, opts = {}, cond = true, version = "*" },
+  {
+    "folke/snacks.nvim",
+    priority = 1000,
+    lazy = false,
+    opts = function()
+      ---@type snacks.Config
+      return {
+        toggle = { map = LazyVim.safe_keymap_set },
+        notifier = { enabled = not LazyVim.has("noice.nvim") },
+        terminal = {
+          win = {
+            keys = {
+              nav_h = { "<C-h>", term_nav("h"), desc = "Go to Left Window", expr = true, mode = "t" },
+              nav_j = { "<C-j>", term_nav("j"), desc = "Go to Lower Window", expr = true, mode = "t" },
+              nav_k = { "<C-k>", term_nav("k"), desc = "Go to Upper Window", expr = true, mode = "t" },
+              nav_l = { "<C-l>", term_nav("l"), desc = "Go to Right Window", expr = true, mode = "t" },
+            },
+          },
+        },
+      }
+    end,
+    keys = {
+      {
+        "<leader>un",
+        function()
+          Snacks.notifier.hide()
+        end,
+        desc = "Dismiss All Notifications",
+      },
+    },
+  },
 }