text: upgrade to CLDR 27.0.1

- CLDR now sports (optional) subversions.
- Added var for the common SerbianLatin locale.
- Allow for UNICODE_VERSION and CLDR_VERSION in internal/gen, as these
  values cannot be passed on the command line to go generate.

Note that the display package simplified and reduced in size. This is
a consequence of that latest version of CLDR reducing the complexity
of the language hierarchy and streamlining some of the differences
between languages.

Change-Id: I086679a73815a7bb0aca099ad73ad43994b57633
Reviewed-on: https://go-review.googlesource.com/9625
Reviewed-by: Nigel Tao <nigeltao@golang.org>
13 files changed