Update Android port

Update Android port

* doc/emacs/android.texi (Android File System): Document new
behavior of starting a subprocess from /assets.
* java/org/gnu/emacs/EmacsWindow.java (onSomeKindOfMotionEvent):
Don't use isFromSource where not present.
* src/androidterm.c (android_scroll_run): Avoid undefined
behavior writing to bitfields.
* src/callproc.c (get_current_directory): When trying to run a
subprocess inside /assets, run it from the home directory
instead.