This is basically commit 363741cf
from 56-based, with the required modifications due to code changes.

Borrowing the original commit message:

ICU 59 changed the UChar type to be char16_t instead of uint16_t and
that causes a mismatch of types all over Chromium.

Unfortunately the upstream patches can not be used as Chromium only
got part way in https://codereview.chromium.org/2740673002

, and
then gave up and simply patched their copy of ICU 59 to not change
that.

Task-number: QTBUG-65090
Change-Id: Icbe46fa33bf56fc3a5aedd5b6004fc029fa24930
Reviewed-by: Jimi Huotari <chiitoo@gentoo.org>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>