We are not looking there anymore, for a long time.

Fixes: #3266

Mention the new --deprecations option of the
validate command.

Note that GtkTreeView is deprecated and link to the
list view introduction from 'Tree and List Widget Overview'.

No need to panic, GTK 5 is still years away!
But it is good to write this material down while
it is fresh in mind.

Make the section about environment variables match
current code.

Add a warning about env vars not being stable and
only for debugging.

The old wiki page has a couple issues:
* It's out-of-date, not having any notes for GTK4 specifically,
  and it doesn't link to `gvsbuild`, which (I believe) is
  the current official (and best) way to build GTK with MSVC.
* It's "locked", so it's harder for contributors to update. This
  is OK, except for one spicy detail:
* It's not clear how to contribute/report issues on the locked wiki
  pages, so out-of-date information falls off the radar.

Regardless :) the gtk.org GTK for Windows docs are a much better
springboard, in my opinion.

Let people know that they will need to use GTK with the Nahimic service
disabled or OpenGL disabled or put their GTK application into the Nahimic
backlist, or try to use GLES, since there is a known issue in the Windows
nVidia graphics drivers and Nahimic that causes GL operations to fail,
causing crashes in operations such as window resizes.

This will close issue #4113--sadly, there is nothing we can do within
GTK to fix the issue.