update Using from Scala 2.13.17 and add UsingTest

fixes #692

copies the sources from scala/scala repo; both `Using` and `UsingTest`
needed slight adjustment to compile on 2.11 and 2.12

includes Scala upgrades: Scala 2.13.17, 2.12.20 (was .13, .19),
Scala.js (because only latest Scala.js is available for 2.13.17)

Author: SethTisue

build.sbt

@@ -50,8 +50,8 @@ lazy val root = project
 lazy val junit = libraryDependencies += "com.github.sbt" % "junit-interface" % "0.13.3" % Test
 
 lazy val scala211 = "2.11.12"
-lazy val scala212 = "2.12.19"
-lazy val scala213 = "2.13.13"
+lazy val scala212 = "2.12.20"
+lazy val scala213 = "2.13.17"
 lazy val scala3 = "3.3.6"
 
 lazy val compat = new MultiScalaCrossProject(
@@ -63,6 +63,9 @@ lazy val compat = new MultiScalaCrossProject(
       moduleName := "scala-collection-compat",
       scalaModuleAutomaticModuleName := Some("scala.collection.compat"),
       scalacOptions ++= Seq("-feature", "-language:higherKinds", "-language:implicitConversions"),
+      // we need to force Scala 3 to use the latest Scala 2 stdlib, otherwise
+      // we might get test failures if there are behavior changes in latest Scala 2 stdlib
+      libraryDependencies += "org.scala-lang" % "scala-library" % scala213,
       Compile / unmanagedSourceDirectories += {
         val sharedSourceDir = (ThisBuild / baseDirectory).value / "compat/src/main"
         CrossVersion.partialVersion(scalaVersion.value) match {