D-Bus support is large, and should have an option to be excluded. Move
the struct implementing D-Bus support from the dispatcher to the main
file, so it can be replaced with a stub.
The D-Bus interfaces used by Phosh are org.gnome.SessionManager for
recovering critical services from crashes and sm.puri.OSK0 for manual
on-screen keyboard activation. Add support for them.
While the keyboard is running, it may want to automatically show or hide
itself depending on whether a text input is active. Add functions to
show and hide the surface by destroying and re-creating it.
Phosh's compositor, phoc, does not emit configure events in reaction to
a surface being committed with no buffer attached. The complicated
surface creation/destruction process is for compatibility with phoc.
