Allow tuples inside square brackets (for list/dict indexing).

--
MOS_MIGRATED_REVID=102841541
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Parser.java b/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
index 7d2311c..8d6f74b 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
@@ -791,7 +791,7 @@
     if (token.kind == TokenKind.COLON) {
       startExpr = setLocation(new IntegerLiteral(0), token.left, token.right);
     } else {
-      startExpr = parseNonTupleExpression();
+      startExpr = parseExpression();
     }
     args.add(setLocation(new Argument.Positional(startExpr), loc1, startExpr));
     // This is a dictionary access