Implement dead key combination on Android

Implement dead key combination on Android

* src/android.c (android_init_key_character_map)
(android_get_dead_char): New functions.
(android_wc_lookup_string): New argument COMPOSE_STATE.  Ignore
key events with the COMBINING_ACCENT flag set while recording
their character values there, and combine such characters with
the key event when processing a subsequent key event.

* src/androidgui.h (struct android_compose_status): New
structure.

* src/androidterm.c (handle_one_android_event): Port dead key
combination code from X.  (bug#69321)