Update Unicode data to Unicode Version 13.0.0
The newest version of Unicode is Unicode 13.0.0 since about one year (see http://www.unicode.org/versions/Unicode13.0.0/). We should finally update Ruby to use Unicode 13.0.0, and probably also backport the result to Ruby 3.0. This issue serves as the main issue for this update; if necessary, I'll create sub-issues.
Currently, I don't expect any major issues (stuff that would require rewriting code) for this upgrade, but I'll check again carefully.
One problem I know of is that Unicode changed the structure of their directories somewhat. This may affect the Ruby makefile infrastructure.