Issue lampepfl#7113: Fix Scala.js codegen for BoxedUnit.TYPE

- `scala.runtime.BoxedUnit.TYPE` is now intercepted by `JSCodeGen` as a
  primitive for `ClassOf(ClassRef("V"))`, which Scala.js recognizes as
  `java.lang.Void`
- Enable the javalib/lang/ClassTest for Scala.js, which contains a test
  that uses `BoxedUnit.TYPE`

Author: Lacaranian

compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala

@@ -2731,6 +2731,8 @@ class JSCodeGen()(implicit ctx: Context) {
 
     if (sym == defn.BoxedUnit_UNIT) {
       js.Undefined()
+    } else if (sym == defn.BoxedUnit_TYPE) {
+      js.ClassOf(jstpe.ClassRef("V"))
     } else {
       val inst = genLoadModule(sym.owner)
       val method = encodeStaticMemberSym(sym)

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -466,6 +466,7 @@ class Definitions {
 
   @tu lazy val BoxedUnitClass: ClassSymbol = ctx.requiredClass("scala.runtime.BoxedUnit")
     def BoxedUnit_UNIT(given Context): TermSymbol = BoxedUnitClass.linkedClass.requiredValue("UNIT")
+    def BoxedUnit_TYPE(given Context): TermSymbol = BoxedUnitClass.linkedClass.requiredValue("TYPE")
 
   @tu lazy val BoxedBooleanClass: ClassSymbol = ctx.requiredClass("java.lang.Boolean")
   @tu lazy val BoxedByteClass   : ClassSymbol = ctx.requiredClass("java.lang.Byte")

project/Build.scala

@@ -978,7 +978,7 @@ object Build {
         val dir = fetchScalaJSSource.value / "test-suite"
         (
           (dir / "shared/src/test/scala/org/scalajs/testsuite/compiler" ** (("*.scala":FileFilter) -- "RegressionTest.scala" -- "ReflectiveCallTest.scala")).get
-          ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/lang" ** (("*.scala": FileFilter) -- "ClassTest.scala" -- "StringTest.scala")).get
+          ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/lang" ** (("*.scala": FileFilter) -- "StringTest.scala")).get
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/io" ** (("*.scala": FileFilter) -- "ByteArrayInputStreamTest.scala" -- "ByteArrayOutputStreamTest.scala" -- "DataInputStreamTest.scala" -- "DataOutputStreamTest.scala" -- "InputStreamTest.scala" -- "OutputStreamWriterTest.scala" -- "PrintStreamTest.scala" -- "ReadersTest.scala" -- "CommonStreamsTests.scala")).get
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/math" ** "*.scala").get
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/net" ** (("*.scala": FileFilter) -- "URITest.scala")).get