libcpp: Update cpp_wcwidth() to Unicode 13.0.0

generated_cpp_wcwidth.h was regenerated using Unicode 13.0.0 data files. No
material changes to the parsing scripts (either GCC- or glibc-sourced) were
necessary; glibc's utf8_gen.py was tweaked slightly by glibc and matched here.

contrib/ChangeLog:

	* unicode/EastAsianWidth.txt: Update to Unicode 13.0.0.
	* unicode/PropList.txt: Likewise.
	* unicode/README: Likewise.
	* unicode/UnicodeData.txt: Likewise.
	* unicode/from_glibc/unicode_utils.py: Update to latest glibc version.
	* unicode/from_glibc/utf8_gen.py: Likewise.

libcpp/ChangeLog:

	* generated_cpp_wcwidth.h: Regenerated from Unicode 13.0.0 data.