RFC: Constant numeric subs for enum and flags values

[Torsten Schoenfeld <kaffeetisch gmx de>]

I've just pushed a branch "enum-constants" which a commit that makes
Glib add constant numeric subs for each value of each enum or flags type
registered with it.  This allows to call Glib::IOCondition::HUP to get
16, or Pango::Weight::BOLD to get 700.

https://git.gnome.org/browse/perl-Glib/log/?h=enum-constants
https://git.gnome.org/browse/perl-Glib/commit/?h=enum-constants&id=361ba7d55f045ea6113479e5798f4213ee7e7dff

This is useful when a function, signal or property expects or returns an
enum or flags value, but the API specification is such that our special
enum and flags string handlers are not invoked. Example: Gtk3::TextTag's
"weight" property accepts any positive integer but predefined values are
given by the Pango::Weight enum.

The downside of supporting this niche application is a slight increase
in load time.  On my machine, I see the following increases for "perl
-M<module> -e0":

  Glib: 1%
  Pango: 3%
  Gtk2: 9%
  Gtk3: 9%

So: Are the benefits of the new functionality worth the increase in load
time?