mirclient/mircommon: rename Configuration to Config to make it consistent with MirDisplayConfig
Note that the affected mircommon headers have not been released yet. The mirclient function name changes have also not been released with 0.25. So this is no ABI/API break that would require a deprecation step.
Mir{Pointer,Touchscreeen,Touchpad,Keyboard}Configuration -> Mir{Pointer,Touchscreeen,Touchpad,Keyboard}Config
mir_input_device_get_pointer_configuration -> mir_input_device_get_pointer_config
mir_input_device_get_touchpad_configuration -> mir_input_device_get_pointer_config
mir_pointer_configuration_* -> mir_pointer_config_*
mir_touchpad_configuration_* -> mir_touchpad_config_*.
Approved by mir-ci-bot, Alan Griffiths, Brandon Schaefer, Cemil Azizoglu.