Add function to create a string from the given code points

[cketti]

CodePoints.toString(…) converts the given code points to a string.

Uses the String constructor supporting code points on the JVM; and a StringBuilder on all other platforms.

[vanniktech]

Would you be open to also provide specialized functions which only take 1, 2, or 3 code points? That way there's no overhead for the vararg. In my case I have quite a lot of usages where varargs would need to be allocated. It's similar to the standard lib which also provides these optimizations:

Roman also wrote about this here.

[cketti]

It wouldn't make a difference on the JVM because the String constructor requires an IntArray.

kotlin-codepoints/kotlin-codepoints/src/jvmMain/kotlin/CodePoints.kt

Lines 46 to 48 in a1d7dbe

	actual inline fun toString(vararg codePoints: Int): String {
	return String(codePoints, offset = 0, length = codePoints.size)
	}

Looking at the StringBuilder implementations for other platforms, I'm guessing optimizing the allocation for the arguments won't yield the biggest return.

But are you really creating strings in a performance-critical loop? If so, you might be better off by reusing a CharArray and calling CharArray.concatToString(startIndex, endIndex).