Implement support for reporting device names on PGTK

Implement support for reporting device names on PGTK

* lisp/frame.el (device-class): Add new function.
* lisp/term/pgtk-win.el (pgtk-device-class): New function.
* src/pgtkterm.c (pgtk_device_added_or_removal_cb)
(pgtk_seat_added_cb, pgtk_seat_removed_cb)
(pgtk_enumerate_devices)
(pgtk_free_devices, pgtk_regenerate_devices)
(pgtk_get_device_for_event): New functions.
(mark_pgtkterm): Mark device data.
(pgtk_delete_terminal): Delete device data.
(pgtk_handle_event, key_press_event, note_mouse_movement)
(construct_mouse_click, button_event, scroll_event)
(drag_data_received): Set device correctly.
(pgtk_term_init): Initialize device data and seat tracking.
(pgtk_delete_display): Delete device data.
* src/pgtkterm.h (struct pgtk_device_t): New struct.
(struct pgtk_display_info): New field `devices'.  Delete lots of
unused macros and reformat comments.