Serve D-Bus and Wayland input method clients

[Azkali]

Fixes https://salsa.debian.org/ubports-team/qtmir/-/work_items/8
Goes along with ubports/development/core/qtmir!168

Adds MALIIT_CONNECTION=dbus|wayland|both. With "both", one maliit-server serves
Qt/Lomiri clients over D-Bus and Wayland clients (GTK, Firefox, Chromium) over
input-method-v1. Without it, behaviour is unchanged.

Needs MALIIT_CONNECTION=both in the session environment (lomiri-session and
lomiri-greeter-wrapper).

[maciek134]

Why would we need this? We should never be in a situation where the DBus API is used/needed when Wayland protocols are used.

Additionally, we need input-method-v2 and work on that is already underway.

[Azkali]

Current situation is that Lomiri runs Qt apps with QT_IM_MODULE=maliit which is D-Bus under the hood. So this was answering to that, now if the plan is to move it all to input-method-v2 which I was unaware of, then yes it is probably best to close this PR once Lomiri also gets the right support