QtWebEngine 5.10.0 fails to build against system ICU >=59.

As far as I can tell, this is, in part, the same issue that was fixed for '56-based', here:

http://code.qt.io/cgit/qt/qtwebengine-chromium.git/commit/?h=56-based&id=363741cffb565dd6cfc2f95054c25a434b101dba

I went through the build fixing failures using said commit as reference, making required changes here and there due to modified code, and additionally added the 'update aspirational_scripts' fix.

I tested only against ICU 60.1, but considering the changes for 56-based, I believe it's at least somewhat safe to guess that the first, bigger patch is needed to fix 5.10 for 59.1, too.