refactor: consolidate per-test subdirectories into flat test/api structure with merged returns and value files

test/api/value.wren

@@ -0,0 +1,14 @@
+class Api {
+  foreign static value=(value)
+  foreign static value
+}
+
+Api.value = ["list", "of", "strings"]
+
+// Do some stuff to trigger a GC (at least when GC stress testing enabled).
+var s = "string"
+for (i in 1...10) {
+  s = s + " more"
+}
+
+IO.print(Api.value) // expect: [list, of, strings]