Add append and prepend operators to the tuple syntax

[danicheg]

The notation of that operators is taken from Scala 3 Tuple methods:
*: — stands for prepend https://github.com/lampepfl/dotty/blob/master/library/src/scala/Tuple.scala#L32
:* — stands for append https://github.com/lampepfl/dotty/blob/master/library/src/scala/Tuple.scala#L26
It'll allow smooth migration on Scala 3 by simply deleting the mouse.tuple._ import.

[danicheg]

@benhutchison it'll be great if you can check this. The implementation is plain as a whole tuple syntax.