inputMethod: Fix delete-surrounding-text signal
Forward the arguments at the 'delete-surrounding-text' signal from IBusInputContext to clutter_input_method_delete_surrounding() so that ibus-typing-booster use the deleting surrounding text function.
Input method engines can delete the output text in applications with this function.
This change will require a change of mutter of mutter!517 (merged) because the first arguemnt of the 'delete-surrounding-text' is INT to express the offset of the current cursor position but the first one of clutter_input_method_delete_surrounding() is UINT since the Wayland spec accepts UINT in delete_surrounding()
mutter will change the type of the first one to INT in clutter_input_method_delete_surrounding() to work with this change.
Edited by Takao Fujiwara