feat(term): ansi: implement ANSI aware truncation

[aymanbagabas]

This implements an ANSI and wide-characters aware truncation algorithm that uses the newly merged ANSI parser state machine and the fantastic library uniseg.

Since this is using the ANSI state machine, it's compatible with CSI m
(SGR) style sequence, OSC 8 (hyperlinks), and basically any other
escape sequence supported in the state machine (DCS, ESC, SOS, PM, APC).

Related: muesli/reflow#71

Benchmarks against reflow truncate.String:

goos: darwin
goarch: amd64
pkg: github.com/charmbracelet/x/exp/term/ansi
cpu: Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
BenchmarkTruncateString-16              41309161                30.61 ns/op           65 B/op          1 allocs/op
BenchmarkReflowTruncateString-16        10123755               119.9 ns/op           291 B/op          3 allocs/op
PASS

func BenchmarkTruncateString(b *testing.B) {
	b.RunParallel(func(pb *testing.PB) {
		b.ReportAllocs()
		b.ResetTimer()
		for pb.Next() {
			Truncate("foo", 2, "")
		}
	})
}

func BenchmarkReflowTruncateString(b *testing.B) {
	b.RunParallel(func(pb *testing.PB) {
		b.ReportAllocs()
		b.ResetTimer()
		for pb.Next() {
			truncate.String("foo", 2)
		}
	})
}