Exporting extension methods drops default arguments

[dcascaval]

Compiler version

3.1.0 (this also reproduces on the latest nightly as of 12/20)

Minimized code

object api:
  export impl.*

object impl:
  class Bar
  extension (rcv: Bar)
    def foo(a: Int) = ()
    def bar(a: Int, b: Boolean = false) = ()

object Test1:
  import api.*
  val value = (new Bar).bar(0) // Error

object Test2:
  import impl.*
  val value = (new Bar).bar(0) // Works

object Test3:
  import api.*
  val value = (new Bar).foo(0) // Works

Output

[error] 12 |  val value = (new Bar).bar(0) // Missing argument
[error]    |              ^^^^^^^^^^^^^^^^
[error]    |missing argument for parameter b of method bar in object api: (a: Int, b: Boolean): Unit

Expectation

Hit this case when exporting extension method through a facade object api from an implementation object impl. Since exporting normal extension methods (e.g. foo) works, I would also expect the method bar to export such that it can be called omitting the second argument and having it be filled in by the default.

[smarter]

3.1.0 (this also reproduces on the latest nightly as of 12/20)

I can't reproduce this with 3.1.2-RC1-bin-20211220-0b55c7d-NIGHTLY, this looks like it was fixed in #14051