A modern programming language that makes developers happier.

kotlinlang

Hi, I would like to contribute to the Kotlin standard library by adding some extension functions to `Pair` and `Triple` for transforming the individual components using a mapping function. This will make the two types more ergonomic to use in a functional programming context. I opened an issue on this <https://youtrack.jetbrains.com/issue/KT-62975/Add-mapping-functions-to-Pair-and-Triple-to-make-functional-style-programming-more-convenient|here> but it seems that there already existed a <https://youtrack.jetbrains.com/issue/KT-21648/Add-mapping-functions-to-Pair-and-Triple|similar issue>.

I'm thinking something like this:

```val x = Pair(1,"Hello")
val y = x.mapSecond { it.length }

println(y) // prints (1, 5)```
The new extension function is `mapSecond`. And there will be a `mapFirst`for Pair also. For Triple I'll add `mapFirst`, `mapSecond` and `mapThird`.

Does this seem like a good idea? What are the chances that a PR will be merged?