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.

NEWS.md

@@ -1,5 +1,19 @@
 # What's new?
 
+## 13.x
+
+- Big new release with a lot of changes and improvements!
+
+- The biggest change is the move of a bunch of core features to
+  [snacks.nvim](https://github.com/folke/snacks.nvim) and fully
+  integrating it into **LazyVim**.
+
+- I highly suggest having a look at the **snacks.nvim** documentation
+  to see all the new features and improvements. Most important changes:
+  - `Snacks.notifier` for notifications instead of `nvim-notify`
+  - `Snacks.terminal` is similar to `lazyterm`, but has more features
+    and creates bottom splits by default (similar to the `edgy` integrating)
+
 ## 12.x
 
 - **Markdown Extra**: [headlines.nvim](https://github.com/lukas-reineke/headlines.nvim) has been removed in favor of [markdown.nvim](https://github.com/MeanderingProgrammer/markdown.nvim)