[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/if_stmt.tolk

@@ -54,13 +54,13 @@ fun main() {
   test3 PROC:<{
     //  x
     DUP	//  x x
-    20 NEQINT	//  x _2
+    20 NEQINT	//  x '2
     IFNOTJMP:<{	//  x
       DROP	//
-      20 PUSHINT	//  _3=20
+      20 PUSHINT	//  '3=20
     }>	//  x
     DUP	//  x x
-    50 EQINT	//  x _5
+    50 EQINT	//  x '5
     IFNOTJMP:<{	//  x
 """
 */