feat: upgrade to gnome 51

Adds GNOME Shell 51 to shell-version and moves the build onto the
GNOME 51 type packages.

- switch to @girs/gjs 5.5.0 and the -51 namespace packages (shell/st/meta/
  clutter plus gio/glib/gobject/gtk/adw)
- drop the @girs/gnome-shell umbrella: it is still GNOME 50 and pulls
  St-18 and Meta-18 types that clash with the -51 packages
- types/: hand-written declarations for the Shell JS modules imported here
  (extension.js, prefs.js, main.js, panelMenu.js, popupMenu.js, slider.js),
  since upstream 51 types (51.0.0-alpha.1) are unpublished. PopupMenu
  open/close are typed with the 51 parameters object
- TypeScript 6.0.3 rather than 7: typescript-eslint requires <6.1.0 and
  ts-jest requires <7
- eslint 10.12, @eslint/js 10.0.1, eslint-plugin-jsdoc 65.3.4 and
  typescript-eslint 8.71.2

tsconfig.json

@@ -14,6 +14,7 @@
   },
   "include": [
     "ambient.d.ts",
+    "types/**/*.d.ts",
     "src/**/*.ts"
   ],
   "exclude": [