bug#30998: 27.0.50; The Help for defclass with multiline documentation is very hard to read

[Xu Chunyang]

I don't know if defclass requires that :documentation must occupies just
a single line. Helm uses many multiple lines string for that slot, please see

https://github.com/emacs-helm/helm/blob/6a34d57f416e4194e6d3207b558d3a00cdf2b955/helm-source.el#L54

'C-h f helm-source' is very hard to read, the following is a part of *Help*

#+BEGIN_EXAMPLE
Instance Allocated Slots:

        Name    Type    Default Doc
        ————    ————    ——————— ———
        name    t       nil       The name of the source.
  A string which is also the heading which appears
  above the list of matches from the source. Must be unique.
        header-name     t       nil       A function returning the display 
string of the header.
  Its argument is the name of the source. This attribute is useful to
  add an additional information with the source name.
  It doesn't modify the name of the source.
        init    t       nil       Function called with no parameters when helm 
is started.
  It is useful for collecting current state information which can be
  used to create the list of candidates later.
  Initialization of `candidates-in-buffer' is done here
  with `helm-init-candidates-in-buffer'.
#+END_EXAMPLE

It seems Emacs is trying to show everything within a table without
considering :documentation can be long.