deps: icu4c 64.2

srl295

Followon to #23244

Platform: all
Subsystem: deps

http://site.icu-project.org/download/64
release candidate today
Unicode 12, CLDR 35

ICU 64 updates to Unicode 12 and to CLDR 35 locale data with many additions and corrections, and some new languages. ICU adds a data filtering/subsetting mechanism, improved formatting API, and a C++ LocaleBuilder.