MFC r339311, r339313:
Restore some of the ctype definitions reported in the PR from pre-CLDR
data, namely 0xE000-0xF8FF private use area, and 0xFF00-0xFFF half- and
fullwidth punctuation.

While here, update tools/tools/locale/README based on my experience
rebuilding the locale data.

PR: 225692
Reviewed by: bapt, cem (previous version)
Differential Revision: https://reviews.freebsd.org/D17471