Fix auto-untupling for generic tuple types

This makes the behaviour of auto-untupling consistent between the usual and
generic tuples.

Related to #23602

Author: EugeneFlesselle

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -280,7 +280,7 @@ object Applications {
         case argType :: Nil
         if args.lengthCompare(1) > 0
             && Feature.autoTuplingEnabled
-            && defn.isTupleNType(argType) =>
+            && (defn.isTupleNType(argType) || argType.isSmallGenericTuple) =>
           untpd.Tuple(args) :: Nil
         case _ =>
           args

tests/pos/generic-untupling.scala

@@ -0,0 +1,8 @@
+
+def foo(x: Option[(Int, Boolean)]) = x match
+  case Some(a, b) => ??? // was ok
+  case None => ???
+
+def bar(x: Option[Int *: Boolean *: EmptyTuple]) = x match
+  case Some(a, b) => ??? // was error, now ok
+  case None => ???