Add forward compatibility check for stdlib-bootstrapped

If we want to use the TASTy of this version of the library with the
binaries generated be the Scala 2.13 compiler, we need to make sure
stdlib-bootstrapped is forwards compatible. For example we can not call
a methods that is available in the dotty compiled version but not in the
Scala 2 compiled version.

Author: nicolasstucki

project/Build.scala

@@ -937,6 +937,8 @@ object Build {
           ).mkString(File.pathSeparator),
         )
       },
+      mimaCheckDirection := "both",
+      mimaBinaryIssueFilters ++= MiMaFilters.LibraryBootstrappedForward,
       run := {
         val args: Seq[String] = spaceDelimited("<arg>").parsed
         val reference = (Compile/sourceManaged).value / "scala-library-src"
@@ -1085,14 +1087,14 @@ object Build {
       (Test / managedClasspath) ~= {
         _.filterNot(file => file.data.getName == s"scala-library-${stdlibVersion(Bootstrapped)}.jar")
       },
-      mimaCheckDirection := "backward",
       mimaPreviousArtifacts +=
         ("org.scala-lang" % "scala-library" % stdlibVersion(Bootstrapped)),
       mimaExcludeAnnotations ++= Seq(
         "scala.annotation.experimental",
         "scala.annotation.specialized",
         "scala.annotation.unspecialized",
       ),
+      mimaCheckDirection := "backward",
       mimaBinaryIssueFilters ++= MiMaFilters.LibraryBootstrapped,
     )