SpringBoot Documentation still has references to 'layertools'

Change layertools to tools Closes https://github.com/spring-projects/spring-boot/issues/43565

Fix @XmlRootElement javadoc links

Reference https://docs.spring.io/spring-boot/how-to/spring-mvc.html#howto.spring-mvc.write-xml-rest-service

Comment From: snicoll

@ngocnhan-tran1996 thanks. Going forward please do not submit two different changes as part of the same PR. I've reverted your fix for the Javadoc and added it as part of #43606.