gnome-base/gnome-shell: bump to 3.26.2, support elogind, many tweaks

gnome-base/gnome-shell: bump to 3.26.2, support elogind, many tweaks

* Port ebuild to use meson (no autotools upstream anymore)
* Support elogind and get rid of unnecessary openrc-force hacks;
  gnome-shell systemd code only handles journald integration - logging
  structured data to it itself, instead of plain g_prints and telling
  it about launched apps, so they get to log under their own identifier
  instead of gnome-session. The -Denable-systemd option only deals with
  that, so we can safely just not pass it on non-systemd systems. The
  suspend support is handled purely via logind dbus interfaces and is
  build unconditionally - at runtime it is conditional on
  /run/systemd/seats existing and being accessible, which should be the
  case with newer elogind (with relevant bugs fixed) by my quick
  research, but I have not tested personally. Don't make a big deal
  about lacking suspend and seat inhibition support and just pull in
  a logind interface provider (techically this is runtime only, but
  not bothering with a separate DEPEND-free RDEPEND block for elogind).
  The alternative (to require logind) would be to require one of the
  systemd or elogind USE flags instead of at-most-one-of, but this is
  runtime optional anyways, so don't block it - user could just build
  with systemd and boot with something else, for example, and similarly
  not have this work at runtime). Also remove some ewarns appropriately.
* Build-time depend on systemd with USE=systemd for the aforementioned
  journald integration, which needs systemd present at build time already.
* More appropriately use python-single-r1 instead of python-r1 for the two
  small python utilities. Hack meson to update to the correct shebang.
* Make telepathy optional - it was made runtime optional in 3.24 already,
  and with empathy being in the state it's in, the chat integration is
  rather unused on a desktop system.
* Remove questionable glib USE=dbus requirement - if dconf is required,
  it should be depended upon directly; but as this is just your typical
  GSettings memory vs dconf backend scenario, I don't see why that'd be.
* Remove unnecessary libXtst depend - I can't find any usage of it in
  current version (only mentions of caribou using it, which has its own
  dep and is optional on-screen keyboard support, gone in newer versions).
* Move dbus-glib depend inside USE=networkmanager, as this legacy thing
  is for some reason (instead of GDbus) still used only in a NM specific
  source file that doesn't get compiled with USE=-networkmanager afaics.
* Require introspection on nm-applet with USE=networkmanager, as NMGtk
  GIR is used.
* Remove bogus mesa-progs depend - no glxinfo/glxgears usages here.
* Add glib-utils build depend.
* Drop dejavu font depend - I don't think we should be pulling in a
  specific font these days for some glyphs; and if we should, then it
  probably should be cantarell.
* Require USE=glib on pulseaudio, as libpulse-mainloop-glib is linked to
  in a subproject, not just libpulse.
* Simplify the pax-mark logic, as we don't use so old spidermonkey for so
  long, and pax-mark stuff is not tested by us. But the old complicated
  conditionals don't apply in many cases, so simplify it to just the common
  case. Additionally newer spidermonkey (60) will lose jit USE flag and
  have that unconditional on arches where it's supported, so these
  conditionals will then result in wrong code paths being taken. Therefore
  just simplify it to the basics and hope it works and rely on any incoming
  bugs about it to modernize this.

Closes: https://bugs.gentoo.org/655426
Closes: https://bugs.gentoo.org/553966
Signed-off-by: Mart Raudsepp <leio@gentoo.org>
Package-Manager: Portage-2.3.49, Repoman-2.3.11