build: Rename meson_options.txt to meson.options

The name is a bit cleaner, and has been the preferred option(!)
since meson 1.1.

Mutter recently updated the name, so follow suite.

The meson version bump shouldn't be an issue, given that several
hard dependencies like mutter and glib already require higher
versions.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/349>
(cherry picked from commit 1088435120)

meson.build

@@ -4,7 +4,7 @@
 
 project('gnome-shell-extensions',
   version: '47.0',
-  meson_version: '>= 0.58.0',
+  meson_version: '>= 1.1.0',
   license: 'GPL2+'
 )