Make FilterRegistrationBean generic

[bclozel]

While trying to fix #7475, it appears that early instantiation is currently the only way to get the type information about the Servlet filter that is about to be created by a FilterRegistrationBean. Doing so in a Condition can cause many initialization issues.

FilterRegistrationBean needs to be made generic, so as to look like FilterRegistrationBean<MyServletFilter>. This will make it easier to the type information without instantiating the bean and will make the registration more expressive about its intent.

[philwebb]

Whilst we're at it we should look at the others as well (ServletRegistrationBean for example).