Fix tab and wide character handling in editor and menu.

	Fix tab and wide character handling in editor and menu.

	* grub-core/normal/charset.c (grub_unicode_aglomerate_comb): Don't
	agglomerate control characters with combining marks.
	(bidi_line_wrap): Allow break on tab.
	(grub_unicode_get_comb_start): New function.
	* grub-core/normal/menu_entry.c: Restructure to handle wide characters
	and tab correctly.
	* grub-core/normal/menu_text.c (print_entry): Replace \n, \r, \b and \e
	with a space.
	* grub-core/normal/term.c (print_ucs4_terminal): New argument
	fixed_tab_size. All users updated.
	* include/grub/term.h (GRUB_TERM_TAB_WIDTH): New const.
	(grub_term_getcharwidth): Handle \t.
	* include/grub/unicode.h (grub_unicode_glyph_dup): Fix allocation
	and copy.