[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/invalid-call-7.tolk

@@ -9,6 +9,6 @@ fun main() {
 
 /**
 @compilation_should_fail
-@stderr undefined symbol `storeUnexisting`
+@stderr non-existing method `storeUnexisting` of type `builder`
 @stderr .storeUnexisting()
  */