Added GeoClue2 privacy item

Rebased onto current master and fixed the privacy module build:
- privacy_item.hpp no longer includes privacy.hpp (it does not use the
  Privacy class); this broke the circular include that left PrivacyItem
  undeclared when privacy.hpp was reached first from privacy_item.cpp.
- privacy_item.cpp now includes gtkmm/label.h explicitly, since Gtk::Label
  was previously only pulled in transitively via privacy.hpp.

meson.build

@@ -426,6 +426,7 @@ if pipewire.found()
         'src/modules/privacy/privacy_item.cpp',
         'src/util/pipewire/pipewire_backend.cpp',
         'src/util/pipewire/privacy_node_info.cpp',
+        'src/util/geoclue_backend.cpp',
     )
     man_files += files('man/waybar-privacy.5.scd')
 endif