Update Android port

Update Android port

* doc/emacs/android.texi (Android File System): Document that
ls-lisp is now used by default.
* java/org/gnu/emacs/EmacsThread.java (EmacsThread): Name the
thread something meaningful.
* lisp/loadup.el (featurep): Load ls-lisp on Android.
* lisp/ls-lisp.el (ls-lisp-use-insert-directory-program):
Default to off on Android.
* src/android.c (android_is_directory): New fucntion.
(android_fstatat): Handle directories created by
`android_opendir'.
(android_open): Return meaningful file mode.
(struct android_dir): New fields `next', `asset_file' and `fd'.
(android_opendir): Populate those fields.
(android_dirfd): New function.
(android_closedir): Close file descriptor if set.
(android_lookup_asset_directory_fd): New function.

* src/android.h: Update prototypes.
* src/androidfont.c (androidfont_check_init): New function.
(androidfont_list, androidfont_match, androidfont_draw)
(androidfont_open_font, androidfont_close_font)
(androidfont_has_char, androidfont_encode_char)
(androidfont_text_extents, androidfont_list_family): Initialize
font driver if necessary.
(init_androidfont): Don't initialize Java font if necessary.

* src/dired.c (open_directory): Return android_dirfd if
appropriate.
(directory_files_internal, file_name_completion_dirp): Implement
correctly for Android.

* src/fileio.c (check_mutable_filename): New function.
(Fcopy_file, Fdelete_directory_internal, Fdelete_file)
(Frename_file, Fadd_name_to_file, Fmake_symbolic_link)
(Fset_file_modes, Fset_file_times, Ffile_newer_than_file_p)
(Fverify_visited_file_modtime, Fset_visited_file_modtime): Check
that files being written to do not lie in /assets.

* src/sfntfont-android.c (GET_SCANLINE_BUFFER)
(sfntfont_android_u255to256, sfntfont_android_over_8888_1)
(sfntfont_android_over_8888, sfntfont_android_composite_bitmap):
Optimize on 64-bit ARM devices.
(sfntfont_android_put_glyphs): Optimize away memset if
background need not be filled.