Fix int/EMACS_INT use in keyboard.c.

Fix int/EMACS_INT use in keyboard.c.

 keyboard.c <last_point_position, last_non_minibuf_size>: Declare EMACS_INT.
 (echo_truncate, adjust_point_for_property, read_char)
 (gen_help_event, make_lispy_event, modify_event_symbol)
 (Fexecute_extended_command, stuff_buffered_input): Use EMACS_INT
 for buffer positions and string length.
 keyboard.h (gen_help_event): Adjust prototype.
 termhooks.h <struct input_event>: Make `code' member EMACS_INT.
 commands.h <last_point_position>: Declare EMACS_INT.
 xdisp.c <help_echo_pos>: Define as EMACS_INT.
 (truncate_echo_area): Accept EMACS_INT argument.
 dispextern.h <help_echo_pos>: Declare EMACS_INT.
 lisp.h (truncate_echo_area): Adjust prototype.
 composite.c (composition_adjust_point): Return EMACS_INT.
 composite.h (composition_adjust_point): Adjust prototype.