Some graphemes (e.g. country flags) break the truncation invariant

[erictheswift]

Considering cli-truncate works with terminal char widths, I think this expectation is valid:
expect(cliTruncate('🇪🇺!', 2)).toEqual('…')

However due to country flags consisting of multiple code points treated as separate chars in slice-ansi, cliTruncate returns "🇪…"

This is not only rendering artifact but a broken invariant, e.g. string-width stringWidth("🇪…") returns 3 that is above requested width 2.

using Intl.Segmenter in slice-ansi can be possible way to fix it: chalk/slice-ansi#35

Got here debugging ink truncation issue when line had country flag on box wrap edge)

[erictheswift]

Also:
require('string-width').default(require('cli-truncate').default('🔀!',2)) // 3