[Tolk] Support syntax tensorVar.0 and tupleVar.0

It works both for reading and writing:
> var t = (1, 2);
> t.0;      // 1
> t.0 = 5;
> t;        // (5, 2)

It also works for typed/untyped tuples, producing INDEX and SETINDEX.

Global tensors and tuples works. Nesting `t.0.1.2` works. `mutate` works.
Even mixing tuples inside tensors inside a global for writing works.

tolk-tester/tests/use-before-declare.tolk

@@ -43,7 +43,7 @@ const demo_20: int = 20;
 """
   test1 PROC:<{
     //
-    30 PUSHINT  // _10
+    30 PUSHINT  // '10
   }>
 """
  */