[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/op-priority.tolk

@@ -95,26 +95,26 @@ fun main() {
   unary_minus_1 PROC:<{
     //  a b c
     -ROT	//  c a b
-    ADD	//  c _3
-    NEGATE	//  c _4
-    SWAP	//  _4 c
-    MUL	//  _5
+    ADD	//  c '3
+    NEGATE	//  c '4
+    SWAP	//  '4 c
+    MUL	//  '5
   }>
   unary_minus_2 PROC:<{
     //  a b c
     -ROT	//  c a b
-    ADD	//  c _3
-    NEGATE	//  c _4
-    SWAP	//  _4 c
-    MUL	//  _5
+    ADD	//  c '3
+    NEGATE	//  c '4
+    SWAP	//  '4 c
+    MUL	//  '5
   }>
   unary_minus_3 PROC:<{
     //  a b c
     -ROT	//  c a b
-    ADD	//  c _3
-    SWAP	//  _3 c
-    MUL	//  _4
-    NEGATE	//  _5
+    ADD	//  c '3
+    SWAP	//  '3 c
+    MUL	//  '4
+    NEGATE	//  '5
   }>
 """