Enable relinquishing access to Android content directories

Enable relinquishing access to Android content directories

* doc/emacs/android.texi (Android Document Providers): Document
new command.

* java/org/gnu/emacs/EmacsService.java (relinquishUriRights):
New function.

* src/Makefile.in (SOME_MACHINE_OBJECTS): Add androidvfs.c.

* src/android.c (android_init_emacs_service): Link to new
function.

* src/android.h (struct android_emacs_service)
<relinquish_uri_rights>: New field.

* src/androidfns.c:

* src/androidvfs.c (android_saf_tree_name)
(android_saf_tree_opendir): Minor adjustments to commentary.
(Fandroid_relinquish_directory_access): New function.
(syms_of_androidvfs): Define new subr.