Support for by-name parameters

[fmonniot]

By name parameters have a different compiler representation than regular functions and need to be handled explicitely in the when macro.

Example:

trait Test:
  def byNameParam(x: => Int): String

val t = mock[Test]
when(t.byNameParam).expect(1).returns("ok")

[fmonniot]

There is still an issue with type inference. The example above works only if we explicitely give the types:

trait Test:
  def byNameParam(x: => Int): String

val t = mock[Test]
when[Int, String](t.byNameParam).expect(1).returns("ok")