Closes https://gitlab.gnome.org/GNOME/evolution-data-server/-/merge_requests/87

The option is still meant to be used in Flatpak only, to prefix
the D-Bus services with certain prefix (usually the same as the Flatpak
application ID), thus the services do not clash with those installed
in the host system. It fixes many issues in evolution-dbus-session.

Related to https://gitlab.gnome.org/GNOME/evolution/issues/165

Handle also cases where the fdlist is only a return value, not an input
argument.

Related to https://gitlab.gnome.org/GNOME/evolution/issues/169

This is required to have properly propagated calls like OpenFile,
which use it.

Related to https://gitlab.gnome.org/GNOME/evolution/issues/169

When an interface contains a D-Bus subtree, then proxy it too, thus
the caller has available everything the interface provides.

The tool runs an isolated D-Bus session, but it also passes D-Bus
messages between the "parent" D-Bus session and the isolated
D-Bus session. It can be used for example by Flatpak applications
to run an isolated D-Bus session for recent evolution-data-server
D-Bus services, while still being able to talk to requested
D-Bus interfaces from the "parent" D-Bus session.

Its build can be enabled with -DENABLE_DBUS_SESSION_TOOL=ON CMake
command argument.

Without the setlocale() call the translated strings were not localized.
Also noticed some strings being marked for localization, but not localized
anyway, thus fixed that too.

And while I’m at it, also spell “MIME” correctly.

See https://developer.gnome.org/hig/stable/typography.html

https://bugzilla.gnome.org/show_bug.cgi?id=774331

Might be useful to check out which sources are known to the source
registry and with its "machine-readable" output mode also parsable
by other tools.