Add tests for experimental imports in experimental scopes

Author: nicolasstucki

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

@@ -0,0 +1,5 @@
+import language.experimental.erasedDefinitions // error // TODO: support
+import annotation.experimental
+
+@experimental
+erased def f = 1

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

@@ -0,0 +1,46 @@
+import annotation.experimental
+
+@experimental
+object Object1:
+  import language.experimental.fewerBraces
+  import language.experimental.namedTypeArguments
+  import language.experimental.genericNumberLiterals
+  import language.experimental.erasedDefinitions
+  erased def f = 1
+
+object Object2:
+  import language.experimental.fewerBraces // error
+  import language.experimental.namedTypeArguments // error
+  import language.experimental.genericNumberLiterals // error
+  import language.experimental.erasedDefinitions // error
+  erased def f = 1
+
+@experimental
+object Class1:
+  import language.experimental.fewerBraces
+  import language.experimental.namedTypeArguments
+  import language.experimental.genericNumberLiterals
+  import language.experimental.erasedDefinitions
+  erased def f = 1
+
+object Class2:
+  import language.experimental.fewerBraces // error
+  import language.experimental.namedTypeArguments // error
+  import language.experimental.genericNumberLiterals // error
+  import language.experimental.erasedDefinitions // error
+  erased def f = 1
+
+@experimental
+def fun1 =
+  import language.experimental.fewerBraces
+  import language.experimental.namedTypeArguments
+  import language.experimental.genericNumberLiterals
+  import language.experimental.erasedDefinitions
+  erased def f = 1
+
+def fun2 =
+  import language.experimental.fewerBraces // error
+  import language.experimental.namedTypeArguments // error
+  import language.experimental.genericNumberLiterals // error
+  import language.experimental.erasedDefinitions // error
+  erased def f = 1