[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-generics-12.tolk

@@ -0,0 +1,15 @@
+fun getTwo<X>(): X { return 2; }
+
+fun cantDeduceNonArgumentGeneric() {
+    var t1: [int] = [0];
+    t1.0 = getTwo();   // ok
+    var t2 = createEmptyTuple();
+    t2.tuplePush(0);
+    t2.0 = getTwo();   // error, can't decude X
+}
+
+/**
+@compilation_should_fail
+@stderr can not deduce X for generic function `getTwo<X>`
+@stderr t2.0 = getTwo();
+ */