Add spread concept code

concept-code/spread.vsm

@@ -0,0 +1,7 @@
+export @_anon0 {}
+
+@_anon0 = function() {
+  mov ["a", "b", "c"] %middle
+  cat [["."], %middle, ["."]] %_tmp0
+  mov %_tmp0 %return
+}

inputs/failing/spread.ts

@@ -0,0 +1,6 @@
+// // test_output! [".","a","b","c","."]
+
+export default function () {
+  const middle = ["a", "b", "c"];
+  return [".", ...middle, "."];
+}