add support for Scala 3

[dwickern]

Play 2.9 supports Scala 3.

• Removes specs2-mock because it does not support Scala 3; see specs2-mock does not support Scala 3 etorreborre/specs2#1156
• swagger-scala-module does not support Scala 3 and the project is archived now. CrossVersion.for3Use2_13 seems to work?

[dwickern]

@gmethvin are these errors expected when compiling for Scala 3? An explicit return type seems to fix it, e.g. def getResources: Action[AnyContent] = ... but I couldn't find anything in the migration guide.

[error] -- [E051] Reference Error: /home/runner/work/swagger-play/swagger-play/src/main/scala/controllers/ApiHelpController.scala:39:34 
[error] 39 |  def getResource(path: String) = Action { implicit request =>
[error]    |                                  ^^^^^^
[error]    |Ambiguous overload. The overloaded alternatives of method apply in trait ActionBuilder with types
[error]    | (block: play.api.mvc.Request[play.api.mvc.AnyContent] => play.api.mvc.Result):
[error]    |  play.api.mvc.Action[play.api.mvc.AnyContent]
[error]    | [A]
[error]    |  (bodyParser: play.api.mvc.BodyParser[A]):
[error]    |    play.api.mvc.ActionBuilder[play.api.mvc.Request, A]
[error]    |both match arguments (<?> => <?>)
[error]    |----------------------------------------------------------------------------
[error]    | Explanation (enabled by `-explain`)
[error]    |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
[error]    | There are 2 methods that could be referenced as the compiler knows too little
[error]    | about the expected type.
[error]    | You may specify the expected type e.g. by
[error]    | - assigning it to a value with a specified type, or
[error]    | - adding a type ascription as in instance.myMethod: String => Int
[error]     ----------------------------------------------------------------------------
[error] Explanation
[error] ===========
[error] There are 2 methods that could be referenced as the compiler knows too little
[error] about the expected type.
[error] You may specify the expected type e.g. by
[error] - assigning it to a value with a specified type, or
[error] - adding a type ascription as in instance.myMethod: String => Int
[error] two errors found
[error] (swaggerplay293 / Compile / compileIncremental) Compilation failed

[gmethvin]

@dwickern Interesting, yeah, that should probably be mentioned in the migration guide, or maybe the API needs to be improved so that doesn't happen.