generate & instead of with if Scala 3

[xuwei-k]

contraband/library/src/main/scala/sbt/contraband/CodecCodeGen.scala

Line 171 in afc4a04

case fms => fms.mkString("self: ", " with ", " =>")

contraband/library/src/main/scala/sbt/contraband/CodecCodeGen.scala

Line 304 in afc4a04

case fms => fms.mkString("self: ", " with ", " =>")

Welcome to Scala 3.5.1 (1.8.0_422, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                                           
scala> trait A; trait B; trait C { self : A with B => }
1 warning found
-- [E003] Syntax Warning: ------------------------------------------------------
1 |trait A; trait B; trait C { self : A with B => }
  |                                     ^^^^
  |                with as a type operator has been deprecated; use & instead

[eed3si9n]

Here's PR for this - #187