2.13.0-M3 error: type Trees$Literal is not a member of package scala.reflect.internal

I have code that uses Trees$Literal, which compiled fine under 2.11 and 2.12. In 2.13.0-M3 I get the error in the title. Did this change? An example full line of code that broke is this:

// Extract MapName annotation if present
val optionalMapName = member.annotations.find(_.tree.tpe =:= typeOf[MapName])
.map { index =>

this got answered at https://stackoverflow.com/questions/48753902/did-treesliteral-reflection-move-in-scala-2-13-0-m3

As sort of explained on Stack Overflow I think it’s correct that the class name Trees$Literal is not accessible in a Scala program because it’s an implementation detail. However I have no idea how or when this got changed.