bug#38598: 26.3; Document relation between `make-symbol` and `gensym`

[Drew Adams <drew.adams@oracle.com>]

(See https://emacs.stackexchange.com/a/54361/105.)

The Common-Lisp doc is clear about the similarity and difference between
`make-symbol` and `gensym`.  The Emacs-Lisp doc says nothing about this.

Please consider mentioning this in (elisp) `Creating Symbols'.  Such
info can help users better understand when they might want to use one or
the other of these functions.

Yes, this info can be gleaned by carefully reading their individual
descriptions (how the symbol-naming is done).  But it would help users
to state it clearly.  The Common-Lisp doc does this simply, with a
single parenthetical sentence: 

  (The only difference between gensym and make-symbol is in how the
  new-symbol's name is determined.)

http://clhs.lisp.se/Body/f_gensym.htm

In GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
 of 2019-08-29
Repository revision: 96dd0196c28bc36779584e47fffcca433c9309cd
Windowing system distributor `Microsoft Corp.', version 10.0.17763
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static -g3''