Use Scala 3 implicit scopes in scalatest

Add `-Yscala3ImplicitScopes` to eneble Scala 3 implicit scope rules under `-language:Scala2`

Author: nicolasstucki

community-build/community-projects/scalatest

@@ -109,6 +109,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val YemitTastyInClass: Setting[Boolean] = BooleanSetting("-Yemit-tasty-in-class", "Generate tasty in the .class file and add an empty *.hasTasty file.")
   val YlogClasspath: Setting[Boolean] = BooleanSetting("-Ylog-classpath", "Output information about what classpath is being applied.")
   val YdisableFlatCpCaching: Setting[Boolean] = BooleanSetting("-YdisableFlatCpCaching", "Do not cache flat classpath representation of classpath elements from jars across compiler instances.")
+  val Yscala3ImplicitScopes: Setting[Boolean] = BooleanSetting("-Yscala3ImplicitScopes", "Use Scala 3 implicit scopes rules under -language:Scala2")
 
   val Yscala2Unpickler: Setting[String] = StringSetting("-Yscala2-unpickler", "", "Control where we may get Scala 2 symbols from. This is either \"always\", \"never\", or a classpath.", "always")
   // TODO: Remove once we drop support for 2.12 standard library

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -268,7 +268,7 @@ object Implicits {
      */
     override val level: Int =
       if (outerImplicits == null) 1
-      else if (ctx.scala2Mode ||
+      else if ((ctx.scala2Mode && !ctx.settings.Yscala3ImplicitScopes.value) ||
                (ctx.owner eq outerImplicits.ctx.owner) &&
                (ctx.scope eq outerImplicits.ctx.scope) &&
                !refs.head.implicitName.is(LazyImplicitName)) outerImplicits.level