define Dsl as public

[i-walker]

fixes when expression with Resource:
currently

when(val x: Resource<Int> = myResource()) {
  is Bind<*,*> -> ...
  is Allocate -> ...
  is Defer -> ...
  is Dsl -> ... // error bc this is internal
  else -> ... // only work around
}

after this PR, the when expression is exhaustive and there is no need to use else:

when(val x: Resource<Int> = myResource()) {
  is Bind<*,*> -> ...
  is Allocate -> ...
  is Defer -> ...
  is Dsl -> 
}