Reorganize tests and benchmark scripts.

Mainly to get rid of one top level directory. But this will
also be useful when there are tests of the embedding API.

test/language/module/change_imported_value/change_imported_value.wren

@@ -0,0 +1,11 @@
+import "module" for Module, Other
+
+IO.print(Module) // expect: before
+
+// Reassigning the variable in the other module does not affect this one's
+// binding.
+Other.change
+IO.print(Module) // expect: before
+
+// But it does change there.
+Other.show // expect: after

test/language/module/change_imported_value/module.wren

@@ -0,0 +1,12 @@
+// nontest
+var Module = "before"
+
+class Other {
+  static change {
+    Module = "after"
+  }
+
+  static show {
+    IO.print(Module)
+  }
+}