QmlJS: Restrict warnings of blocks

Warn only if the block contains a var statement
as this is discouraged.

Fixes: QTCREATORBUG-24214
Change-Id: Ib96c6723e82b6ddce0b7b63f23d3408f45ae7d58
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/libs/qmljs/qmljscheck.h

@@ -123,6 +123,7 @@ private:
     bool isQtQuick2Ui() const;
 
     bool isCaseOrDefault(AST::Node *n);
+    bool hasVarStatement(AST::Block *b) const;
 
     AST::Node *parent(int distance = 0);