refactor!: replace all-the-icons with nerd-icons

BREAKING CHANGE: This commit replaces all-the-icons with nerd-fonts. Any
all-the-icons-* function calls or variable references in your private
config will break and should be replaced with their nerd-icons-*
equivalent. That said, Doom will continue to install all-the-icons for
a while, so feel free to load it if you don't want to fully commit to
the change yet.

This change is happening because nerd-icon has wider support for GUI and
TUI Emacs; has a larger, more consistent selection of symbols; plus unicode
coverage.

Fix: #7368
Close: #6675
Close: #7364

lisp/lib/system.el

@@ -52,8 +52,8 @@
   (with-memoization (get 'doom-system-distro-icon 'cached-value)
     (propertize
      (pcase (doom-system-distro)
-       (`windows (all-the-icons-faicon "windows"))
-       (`macos (all-the-icons-faicon "apple"))
+       (`windows (nerd-icons-faicon "nf-fa-windows"))
+       (`macos (nerd-icons-faicon "nf-fa-apple"))
        (`arch "\uF303")
        (`debian "\uF306")
        (`raspbian "\uF315")
@@ -74,7 +74,7 @@
        (`devuan "\uF307")
        (`manjaro "\uF312")
        ((or `void `artix) "\uF17c")
-       (_ (all-the-icons-faicon "linux")))
+       (_ (nerd-icons-faicon "nf-fa-linux")))
      'face '(:height 1)
      'display '(raise 0))))