term/eshell: fix eshell resetting eshell-mode-map

This "backports" a Emacs 28 fix which prevents eshell from resetting
eshell-mode-map every time eshell-mode is activated.

Now users can bind keys to eshell-mode-map like they could for any
normal mode.

modules/term/eshell/config.el

@@ -118,11 +118,6 @@ You should use `set-eshell-alias!' to change this.")
             (append eshell-command-aliases-list
                     +eshell-aliases))))
 
-  (add-hook! 'eshell-first-time-mode-hook
-    (defun +eshell-init-keymap-h ()
-      ;; Keys must be bound in a hook because eshell resets its keymap every
-      ;; time `eshell-mode' is enabled. Why? It is not for us mere mortals to
-      ;; grasp such wisdom.
   (map! :map eshell-mode-map
         :n "RET"     #'+eshell/goto-end-of-prompt
         :n [return]  #'+eshell/goto-end-of-prompt
@@ -150,7 +145,17 @@ You should use `set-eshell-alias!' to change this.")
         (:localleader
          "b" #'eshell-insert-buffer-name
          "e" #'eshell-insert-envvar
-             "s" #'+eshell/search-history)))))
+         "s" #'+eshell/search-history))
+
+  ;; HACK Eshell resets its keymap every time `eshell-mode' is enabled. Why? It
+  ;;      is not for us mere mortals to question! Fun fact: there's a "FIXME
+  ;;      What the hell?!" above the offending line in esh-mode.el.
+  ;; DEPRECATED As of Emacs 28, binding keys in a hook is no longer necessary.
+  (add-hook! 'eshell-mode-hook
+    (defun +eshell-fix-keymap-h ()
+      "Undo buffer-local `eshell-mode-map', so global keybinds work."
+      (kill-local-variable 'eshell-mode-map)
+      (use-local-map eshell-mode-map))))
 
 
 (use-package! eshell-up