Log4jWebConfigurer supports resolving placeholders against ServletContext init-parameters as well

Introducing a ServletContextPropertyUtils helper (analogous to SystemPropertyUtils) along the way.

Issue: SPR-10284
Fixed @Configurable documentation with respect to the use of a prototype-scoped bean definition.

Issue: SPR-10298
Removed outdated EJB reference from auto-proxying documentation.

Issue: SPR-10299
Fixed @Configurable documentation with respect to logging when the aspect hasn't been configured

Issue: SPR-10295