ElDoc: Add more commands using 'eldoc-add-command-completions'

Add more commands to 'eldoc-add-command-completions' to fix
disappearing ElDoc help in the minibuffer for the following
cases:
- All modes: Added "comment-indent-new-line".
- All modes: Added "delete-char" for handling when the user presses delete.
- Python mode: Added "python-indent-dedent-line-backspace" for handling
  when the user presses backspace.
* lisp/emacs-lisp/eldoc.el (eldoc-remove-command-completions):
* lisp/progmodes/python.el (python-base-mode): Add more commands
to 'eldoc-add-command-completions'.

Copyright-paperwork-exempt: yes

lisp/emacs-lisp/eldoc.el

@@ -994,7 +994,7 @@ the docstrings eventually produced, using
 
 ;; Prime the command list.
 (eldoc-add-command-completions
- "back-to-indentation"
+ "comment-indent-new-line" "delete-char" "back-to-indentation"
  "backward-" "beginning-of-" "delete-other-windows" "delete-window"
  "down-list" "end-of-" "exchange-point-and-mark" "forward-" "goto-"
  "handle-select-window" "indent-for-tab-command" "left-" "mark-page"

lisp/progmodes/python.el

@@ -7147,6 +7147,7 @@ implementations: `python-mode' and `python-ts-mode'."
           (add-hook 'eldoc-documentation-functions #'python-eldoc-function nil t)
         (add-function :before-until (local 'eldoc-documentation-function)
                       #'python-eldoc-function))))
+  (eldoc-add-command-completions "python-indent-dedent-line-backspace")
 
   ;; TODO: Use tree-sitter to figure out the block in `python-ts-mode'.
   (dolist (mode '(python-mode python-ts-mode))