Update to ICU 68.1

ICU 68.1 release notes: http://site.icu-project.org/download/68
CLDR 38: release notes: http://blog.unicode.org/2020/10/unicode-cldr-language-data-v38-released.html

1. Update to 68-1
   Diary
https://docs.google.com/document/d/1fnMrx4aaVZJlVoFNFrJTXvolLGXA4aQS3vEMcAmPvrs/edit#

Size changes:
 before     68-1
 7869568  8187056 android/icudtl.dat
 6510048  6517696 android_small/icudtl.dat
 1498144  1801520 android_small/icudtl_extra.dat
 5059104  4911056 cast/icudtl.dat
10618064 10502448 chromeos/icudtl.dat
10527920 10413552 common/icudtb.dat
10527920 10413552 common/icudtl.dat
  898416 . 799760 flutter/icudtl.dat
 6463792  6322896 ios/icudtl.dat

2. This landing includes
a) Cherrypick the works on the staging68 branch by
$ git rev-list --reverse 84fb34e2d..3e828e7 | xargs git cherry-pick --strategy=recursive -X theirs

See
https://chromium.googlesource.com/chromium/deps/icu/+log/84fb34e2d..3e828e7

b) Fix copy_data.sh to generate common/icudtb.dat

c) Rebuild the data file

3. Testing CLs with the hash on the staging68: 3e828e72
chrome DEPS: https://chromium-review.googlesource.com/c/chromium/src/+/2474093
v8 DEPS: https://chromium-review.googlesource.com/c/v8/v8/+/2477431


Bug: 1138555
TBR=jshin@chromium.org
Change-Id: Iac5d712f11fb740d9f90ee033bc2cf6304193a1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/2473347
Reviewed-by: Frank Tang <ftang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/2511803
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/icu/+/449856
Reviewed-by: Fabrice de Gans-Riberi <fdegans@google.com>
4640 files changed