Log Message:
Update to 57.1

Changelog:
Common Changes
    CLDR 29: For details of the many changes in CLDR, see CLDR 29.
    Grapheme/word/line breaking for emoji sequences, based on Unicode 9 proposed \ 
rules. See the Unicode emoji break proposal and the Unicode Emoji Technical \ 
Report Proposed Update describing the new emoji sequences.  (#12081).
    Four new Unicode emoji properties (#11802).
    DateFormat day period formatting of "noon", "at night", \ 
etc. via new pattern characters b & B, and DateTimePatternGenerator support \ 
of C for selecting the customary form (#11872).
        Except: Formatting of "0:00 midnight" has been disabled \ 
because it is confusing except for at the end of an interval.
    RelativeDateTimeFormatter: Simpler formatting API (#12072).
    More robust CLDR data loading for MeasureFormat (#11986, #12030), \ 
RelativeDateTimeFormatter (#12018), and DateIntervalFormat/DateIntervalInfo \ 
(#12013).
    New simple & fast SimpleFormatter class for a trivial subset of \ 
MessageFormat as used in CLDR data, e.g., "{0} {1}" (#10896).

ICU4C Specific Changes
    C API support for RelativeDateTimeFormatter (#12072).
    Clang annotations for intended switch case fallthroughs, can now compile \ 
with -Wimplicit-fallthrough (#12166).
    Internal header files can be compiled by themselves, for simpler alternative \ 
build scripts (#12141).