Integrate full Log4j 2 support into Spring Boot

[rgoers]

This change merges the contents of the log4j-spring-boot module into Spring Boot, effectively making Log4j 2 on par with Logback and eliminating the need for the log4j-spring-boot module.

I was able to verify this with a sample project I have. While the project doesn't fully run (it hasn't completely converted to Spring 3) it did get far enough along to verify that I could successfully retrieve the logging configuration from Spring Cloud Config server using basic password authentication and resolve the application name using the SpringLookup.

Note: This requires Log4j 2.19.0. While building I discovered there were tests that were hard-coded to older versions of Log4j 2. These had to be modified to reference version 2.19.0 as they no longer work. Those older versions shouldn't be supported with Spring 3 in any case.