Can't call generic method with array of value type

[abeln]

If we have Java code

class Foo {
  public static<T> void foo(T[] arr) {}
}

we can no longer call it from Scala with an argument that's an array of a value type

class Bar { // in Scala
  val arr: Array[Int] = ???
  Foo.foo(arr) // error: expected Array[Int|JavaNull]|JavaNull, but got Array[Int]
}

Instead, we need to make arr nullable: val arr: Array[Int|Null] = ???, which is bad for performance. Pre explicit nulls, this used to work because the array was automatically copied to an Array[Object] at the callsite.

See https://github.com/abeln/dotty/commit/59671f7e86ee68dddf21016b3e0b5acdc0371e90#diff-459714fae8d4a9d0faf4dee5e40a5b2dR1 for the test that motivated this.

[abeln]

@olhotak do you remember what we agreed for this one?