phase: 20.49 COMPLETE; 20.50 Flow+String minimal reps; 20.51 selfhost v0/v1 minimal (Option A/B); hv1-inline binop/unop/copy; docs + run_all + CURRENT_TASK -> 21.0

apps/tmp_len_test2.hako

@@ -0,0 +1,10 @@
+static box Main {
+  main() {
+    local S
+    using "apps/std/string2.hako" as S
+    local x
+    x = S.string_length("abc")
+    print("len=" + x.toString())
+    return 0
+  }
+}