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).

(ryoon)