Updated to latest Unicode spec 15.1.0 and set version to 1.4.0

[erf]

I ran tool/generate.dart to update to the latest Unicode spec 15.1.0.

I ran tests and benchmarks OK.

I set the CHANGELOG.md and pubspec.yaml to version 1.4.0

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[kevmoo]

@lrhn – wanna take a look?

[lrhn]

I don't think this update is needed.

While Unicode 15.1 introduces new emoji combinations, it does that by assigning a meaning to combinations that can already be made today. It doesn't change how to break the text into grapheme clusters.

If there is no difference between Unicode 15.0 and Unicode 15.1 in the grapheme cluster segmentation, it means there is no difference in the generated tables, which is also what we see. That means that there is no functional change, and no need to change anything. All this PR does is change "15.0.0" to "latest" in a comment, which isn't really an improvement (I should try to make it write the actual number instead of current), and reformats the generated test file, which seems to show a difference in dart format, not content.

[erf]

I see. Feel free to close.