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/number/bitwise_not.wren

@@ -0,0 +1,22 @@
+IO.print(~0) // expect: 4294967295
+IO.print(~1) // expect: 4294967294
+IO.print(~23) // expect: 4294967272
+
+// Max u32 value.
+IO.print(~4294967295) // expect: 0
+
+// Past max u32 value.
+IO.print(~4294967296) // expect: 4294967295
+
+// Negative numbers.
+IO.print(~-1) // expect: 0
+IO.print(~-123) // expect: 122
+IO.print(~-4294967294) // expect: 4294967293
+IO.print(~-4294967295) // expect: 4294967294
+IO.print(~-4294967296) // expect: 4294967295
+
+// Floating point values.
+IO.print(~1.23) // expect: 4294967294
+IO.print(~0.00123) // expect: 4294967295
+IO.print(~345.67) // expect: 4294966950
+IO.print(~-12.34) // expect: 11