The REPL guide should be part of the Scala Book

We would like the [Scala Book](https://docs.scala-lang.org/scala3/book/introduction.html) to be a complete documentation of the language.

The content [REPL](https://docs.scala-lang.org/overviews/repl/overview.html) should be merged into the Scala Book, which also contains a [REPL](https://docs.scala-lang.org/scala3/book/taste-repl.html) page.