SpringBoot Polish 'AbstractServletWebServerFactory.configureSessionCookie()'

Polish AbstractServletWebServerFactory with PropertyMapper.

Comment From: snicoll

@weixsun thanks again for the PR. This looked very sensible but it actually broke the build. This change turned out to reveal, I think, a problem in our test setup. I have opened #26479 to investigate.

Comment From: snicoll

Thanks again @weixsun