Our Singular interface currently contains a hand-written parser for Singular's "info" file. In this ticket, we add an optional GNU Info package to parse this file instead.

Relative to running "info", the hand-written parser has several drawbacks:

• The extra code is a maintenance burden. We should not be wasting
  our time (poorly) reimplementing standard tools.

• The custom parser is buggy. For example, it is supposed to raise a
  KeyError when documentation for a non-existent function is
  requested. However, the parser does not keep track of what section
  it's in, so, for example, get_docstring("Preface") will happily
  return the contents of the preface even though "Preface" is not a
  Singular function.

• The first time documentation is requested, the entire info file
  (see above) is loaded into a dictionary. With the Singular info
  file currently weighing in at around 11MiB, this is wasting a
  good chunk of memory.

• The singular_console() itself tries to launch GNU Info to display
  its interactive help, and cannot use our hand-written parser.

The one downside to requiring "info" is that it would add a new runtime dependency to sagelib. To avoid that, we make GNU Info optional, and suggest to the user that he install it when he tries to read Singular's documentation.

GNU Info (or its superset, Texinfo) are widespread, portable, and easy to install on all of the systems we support, so in most cases this should be a "free" improvement.

Depends on #32302

Component: packages: standard

Author: Michael Orlitzky

Branch/Commit: u/mjo/ticket/32242 @ 137a918

Issue created by migration from https://trac.sagemath.org/ticket/32242