Implicit conversions to refinements of Any/AnyVal/AnyRef should be allowed

[sjrd]

Minimized code

import scala.reflect.Selectable.reflectiveSelectable

object Test {
  def main(args: Array[String]): Unit = {
    def fCompareToBoolean(x: { def compareTo(y: java.lang.Boolean): Int }, y: Boolean): Int =
      x.compareTo(y)
    assert(fCompareToBoolean(false, true) < 0)
  }
}

Output

-- Error: tests/run/hello.scala:7:29 -------------------------------------------
7 |    assert(fCompareToBoolean(false, true) < 0)
  |                             ^^^^^
  |the result of an implicit conversion must be more specific than Object{compareTo(y: Boolean): Int}
1 error found

Expectation

The code compiles and runs successfully, as it does on Scala 2.

Notes

Implicit conversions to Any/AnyVal/AnyRef were disallowed in #8453 to fix the issue #6336. Apparently the introduced check was too strict, as it also disallows implicit conversions to refinements, which Scala 2 doesn't do.

This was discovered while trying to enable the Scala.js test ReflectiveCallsTest.scala, but the issue arises on the JVM as well.