feat(keymaps): dynamic which-key icons/descriptions for toggles (#4050)

## Description

<!-- Describe the big picture of your changes to communicate to the
maintainers
  why we should accept this pull request. -->

## Related Issue(s)

- [ ] Closes #4025

## Screenshots


![image](https://github.com/user-attachments/assets/8453c23c-d560-490c-9f96-a22ea88f45fd)

## Checklist

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

lua/lazyvim/plugins/treesitter.lua

@@ -1,4 +1,14 @@
 return {
+  {
+    "folke/which-key.nvim",
+    opts = {
+      spec = {
+        { "<BS>", desc = "Decrement Selection", mode = "x" },
+        { "<c-space>", desc = "Increment Selection", mode = { "x", "n" } },
+      },
+    },
+  },
+
   -- Treesitter is a new parser generator tool that we can
   -- use in Neovim to power faster and more accurate
   -- syntax highlighting.