The GIMP_VIEW_SIZE_ENORMOUS enum setting was missing from
the Preview Size menu. This patch adds it in so that users have a
preview size option between Extra Large and Enormous.
Depending on where it's used, this list of action can be either in the
"dockable" or the "dialogs" action group.
The meson rule is a bit more complicated than I wished it were because of the
ever-so-blocking lack of simple dependency in meson.
Cf. my latest comment: https://github.com/mesonbuild/meson/issues/8123#issuecomment-1496168759