Add a configure event to zwp_input_panel_v1

When displaying an input panel, the compositor may sometimes want to adjust the placement and size of the input panel, for example to account for a task bar or other shell surface that the input panel may overlap. While placement is already done by the compositor, currently there is no way to communicate a desired size to the input panel client, so sizing is not possible.

This adds a configure event to zwp_input_panel_v1, allowing the compositor to request a new panel size from the input panel client. A corresdponding ack_configure request is also added so the client can let the compositor know it processed the configure.