Add more tests

# Conflicts:
#	tests/neg-custom-args/no-experimental/experimental.scala

Author: odersky

tests/neg-custom-args/no-experimental/experimental.scala

@@ -2,24 +2,33 @@ class Test0 {
   import language.experimental.namedTypeArguments // error
   object Foo {
     inline def f[S, T](x: S): T = ???
-    def g(x: Int) = f[T = Any](x)                 // error
+    def g(x: Int) = f[T = Any](x)
   }
 }
 
 class Test1 {
-  import language.experimental.erasedDefinitions  // error
+  import scala.language.experimental.erasedDefinitions  // error
   import scala.compiletime.erasedValue
   type UnivEq[A]
   object UnivEq:
-    erased def force[A]: UnivEq[A] = erasedValue  // error // error // error
-    extension [A](erased proof: UnivEq[A])        // error
+    erased def force[A]: UnivEq[A] = erasedValue
+    extension [A](erased proof: UnivEq[A])
       inline def univEq(a: A, b: A): Boolean =
         a == b
 }
 
-class Test1 {
-  import language.experimental.genericNumberLiterals // error
+class Test2 {
+  import _root_.scala.language.experimental.{genericNumberLiterals, namedTypeArguments => _} // error
   val x: BigInt = 13232202002020202020202
   val y: BigInt = -0xaabb12345ACF12345AC
 }
 
+class Test6 {
+  import scala.language.experimental  // ok
+}
+
+class Test7 {
+  import scala.language.experimental
+  import experimental.genericNumberLiterals // error: no aliases can be used to refer to a language import
+  val x: BigInt = 13232202002020202020202   // error
+}