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/shared_import/a.wren

@@ -0,0 +1,5 @@
+// nontest
+IO.print("a")
+import "shared" for Shared
+var A = "a " + Shared
+IO.print("a done")

test/language/module/shared_import/b.wren

@@ -0,0 +1,5 @@
+// nontest
+IO.print("b")
+import "shared" for Shared
+var B = "b " + Shared
+IO.print("b done")

test/language/module/shared_import/shared.wren

@@ -0,0 +1,3 @@
+// nontest
+IO.print("shared")
+var Shared = "shared"

test/language/module/shared_import/shared_import.wren

@@ -0,0 +1,12 @@
+import "a" for A
+import "b" for B
+
+// Shared module should only run once:
+// expect: a
+// expect: shared
+// expect: a done
+// expect: b
+// expect: b done
+
+IO.print(A) // expect: a shared
+IO.print(B) // expect: b shared