I've found the dependencies I need to add to the pom.xml so that FormsHelper class is available:
<dependency> <groupId>com.adobe.granite</groupId> <artifactId>com.adobe.granite.xssprotection</artifactId> <version>5.5.62</version> <scope>provided</scope> </dependency> <dependency> <groupId>com.day.cq.wcm</groupId> <artifactId>cq-wcm-foundation</artifactId> <version>5.8.52</version> <scope>provided</scope> </dependency>