Ensure Array[? >: AnyRef] erases to Object[]

Fixes #23179

Since JDK 9, argument checks for LambdaMetaFactory have become stricter.
Which is to say that its JDK 8 version was too lax.

We now align with Scala 2's behavior and erase `Array[? >: AnyRef]`
to `Object[]` instead of just `Object`. This seems consistent with
how we handle `Array[Any]`, which also erases to `Object[]`.

Author: bracevac

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

@@ -361,6 +361,7 @@ object TypeErasure {
         isGenericArrayElement(tp.alias, isScala2)
       case tp: TypeBounds =>
         !fitsInJVMArray(tp.hi)
+        && !(tp.lo.isAnyRef && tp.hi.isAny) // #23179, aligns with Scala 2 behavior for Array[? >: AnyRef]
       case tp: MatchType =>
         val alts = tp.alternatives
         alts.nonEmpty && !fitsInJVMArray(alts.reduce(OrType(_, _, soft = true)))

tests/run/i23179.scala

@@ -0,0 +1,8 @@
+object Test {
+  trait A { def f(a: Array[AnyRef]): Any }
+  def g(a: A) = a.f(Array.empty[AnyRef])
+
+  def main(args: Array[String]): Unit = {
+    g((x: Array[? >: AnyRef]) => x.headOption)
+  }
+}