[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/symtable.cpp

@@ -126,6 +126,18 @@ SymDef* define_global_symbol(sym_idx_t name_idx, SrcLocation loc) {
   return registered;  // registered->value is nullptr; it means, it's just created
 }
 
+SymDef* define_parameter(sym_idx_t name_idx, SrcLocation loc) {
+  // note, that parameters (defined at function declaration) are not inserted into symtable
+  // their SymDef is registered to be inserted into SymValFunc::parameters
+  // (and later ->value is filled with SymValVariable)
+
+  SymDef* registered = new SymDef(0, name_idx, loc);
+#ifdef TOLK_DEBUG
+  registered->sym_name = registered->name();
+#endif
+  return registered;
+}
+
 SymDef* define_symbol(sym_idx_t name_idx, bool force_new, SrcLocation loc) {
   if (!name_idx) {
     return nullptr;