Finer grained word boundaries for the REPL's line editor
Finer grained word boundaries for the REPL's line editor

Adapted from https://github.com/scala/scala/pull/9017, this lets you edit:

```
scala> this.toString<ALT-BACKSPACE>
```

To:

```
scala> this.
```

Co-Authored-By: Jason Zaugg <8287c3bf2f3045ed7dda958850d2b0fdb9e67898@gmail.com>

lampepfl/dotty,sjrd/dotty,lampepfl/dotty,sjrd/dotty,dotty-staging/dotty,sjrd/dotty,dotty-staging/dotty,lampepfl/dotty,dotty-staging/dotty,dotty-staging/dotty,lampepfl/dotty,sjrd/dotty,dotty-staging/dotty,lampepfl/dotty,sjrd/dotty