Update list of regions to Unicode

[behdad]

Unicode now defines which regions are emoji flags. According to Mark Davis:

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The valid flags used to be less clearly specified, but they are defined in the newest (v2.0) spec, http://unicode.org/reports/tr51/

ED-14. emoji flag sequence — A sequence of two Regional Indicator characters, where the corresponding ASCII characters are valid region sequences as specified by Unicode region subtags in [CLDR].

Those Unicode region subtags are based on BCP47, but have some small changes (including http://unicode.org/emoji/charts/full-emoji-list.html#1f1fd_1f1f0The valid flags used to be less clearly specified, but they are defined in the newest (v2.0) spec, http://unicode.org/reports/tr51/

ED-14. emoji flag sequence — A sequence of two Regional Indicator characters, where the corresponding ASCII characters are valid region sequences as specified by Unicode region subtags in [CLDR].

Those Unicode region subtags are based on BCP47, but have some small changes (including http://unicode.org/emoji/charts/full-emoji-list.html#1f1fd_1f1f0

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We should switch to this instead of BCP 47 itself.

[xiangyexiao]

@dougfelt