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.
The Held state is for modifier that should be off when the corresponding
key is released. If the user presses the modifier key and a normal key,
it would be in this state. The modifier would continue to be active when
the user moves to a different key part (a cancel, e.g. from Fn to Alt)
afterwards. To fix this, add the HeldPressed and HeldLockedPressed
states that reset to the Released state when cancelled.
Keeping the keys pressed can confuse some compositors, and the key codes
may change. Release any keys that are pressed while the keymap is
changing, and press them again afterwards.
When the surface attaches to a buffer, all other buffers are available.
Export the function used to release a buffer, track the buffer used by
the surface, and release unused buffers when a new buffer is attached.
