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Instead of individual tests for tag sequences, use newer ICU methods to
detect xpicto_sequences as in Unicode TR#29, compare
https://www.unicode.org/reports/tr29/#Regex_Definitions by using ICU's
UCHAR_EMOJI_COMPONENT and UCHAR_EMOJI_COMPONENT checks.

Bug: 1121420
Change-Id: I37c9cab51ea88c6be85c2df637af03dcf68c568f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2390341Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804168}