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/core/map/count.wren

@@ -0,0 +1,12 @@
+var map = {}
+IO.print(map.count) // expect: 0
+map["one"] = "value"
+IO.print(map.count) // expect: 1
+map["two"] = "value"
+IO.print(map.count) // expect: 2
+map["three"] = "value"
+IO.print(map.count) // expect: 3
+
+// Adding existing key does not increase count.
+map["two"] = "new value"
+IO.print(map.count) // expect: 3