Revert <: Product requierment in pattern matching

The change in question broke the following pattern, commonly used in name based pattern matching:

```scala
object ProdEmpty {
  def _1: Int = ???
  def _2: String = ???
  def isEmpty = true
  def get = this
}
```

This type define both `_1` and `get` + `isEmpty` (but is not <: Product). After #1938, `ProdEmpty` became eligibles for both product and name based pattern. Because "in case of ambiguities, *Product Pattern* is preferred over *Name Based Pattern*", isEmpty wouldn't be used, breaking the scalac semantics.

1 files changed, 37 insertions, 0 deletions

diff --git a/tests/run/1938-2.scala b/tests/run/1938-2.scala
new file mode 100644
index 000000000..32e4c4518
--- /dev/null
+++ b/tests/run/1938-2.scala
@@ -0,0 +1,37 @@
+object ProdNonEmpty {
+  def _1: Int = 0
+  def _2: String = "???" // Slight variation with scalac: this test passes
+                         // with ??? here. I think dotty behavior is fine
+                         // according to the spec given that methods involved
+                         // in pattern matching should be pure.
+  def isEmpty = false
+  def unapply(s: String): this.type = this
+  def get = this
+}
+
+object ProdEmpty {
+  def _1: Int = ???
+  def _2: String = ???
+  def isEmpty = true
+  def unapply(s: String): this.type = this
+  def get = this
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    "" match {
+      case ProdNonEmpty(0, _) => ()
+      case _ => ???
+    }
+
+    "" match {
+      case ProdNonEmpty(1, _) => ???
+      case _ => ()
+    }
+
+    "" match {
+      case ProdEmpty(_, _) => ???
+      case _ => ()
+    }
+  }
+}