update widechar part and tests from ncurses 5.9

Change-Id: I63e1ba135c65e4818b4891763cc6999510a3a0dd
utf8: add custom string mb to wc convert funcs

Change-Id: Ib0265cd7da7e0d247d11250bc340ed03439bcd64
Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>