bug#58324: 28.1: Variable-name error in documentation of variables used to configure ElDoc mode

[Mark Harig]

In the Emacs info manual, (emacs) Lisp Doc, one of the variables
documented is `eldoc-display-truncation-message'.  But C-h v is
unable to reference this variable to provide its description.
Instead, in the Eldoc customization group, there is the variable
named `eldoc-echo-area-display-truncation-message', whose
description appears to match the description at the (emacs) Lisp
Doc node of the Emacs info manual.

If this is the intended variable name, then the Emacs info manual
needs to be changed to use it.

(End of report.)