SI-7737 Regex matches Char

Enables Char extraction by regex.

```
val r = """(\p{Lower})""".r
"cat"(0) match { case r(x) => true }
val nc = """\p{Lower}""".r
"cat"(0) match { case nc() => true }
```
Merge pull request #2819 from som-snytt/issue/regextract-char

SI-7737 Regex matches Char