[Tolk] Get rid of ~tilda with mutate and self methods

This is a very big change.
If FunC has `.methods()` and `~methods()`, Tolk has only dot,
one and only way to call a `.method()`.
A method may mutate an object, or may not.
It's a behavioral and semantic difference from FunC.

- `cs.loadInt(32)` modifies a slice and returns an integer
- `b.storeInt(x, 32)` modifies a builder
- `b = b.storeInt()` also works, since it not only modifies, but returns
- chained methods also work, they return `self`
- everything works exactly as expected, similar to JS
- no runtime overhead, exactly same Fift instructions
- custom methods are created with ease
- tilda `~` does not exist in Tolk at all

tolk/analyzer.cpp

@@ -46,10 +46,9 @@ int CodeBlob::split_vars(bool strict) {
     if (k != 1) {
       var.coord = ~((n << 8) + k);
       for (int i = 0; i < k; i++) {
-        auto v = create_var(vars[j].is_tmp_unnamed, comp_types[i], 0, vars[j].where);
+        auto v = create_var(comp_types[i], vars[j].sym_idx, vars[j].where);
         tolk_assert(v == n + i);
         tolk_assert(vars[v].idx == v);
-        vars[v].name = vars[j].name;
         vars[v].coord = ((int)j << 8) + i + 1;
       }
       n += k;