Use Log4jBridgeHandler to route JUL-based logging into Log4j 2

Since version 2.15.0 `log4j-jul` contains a `Log4jBridgeHandler`,
that forwards JUL to Log4j 2.x and synchronizes the logger levels of
the two frameworks.

This commmit adds support for the `Log4jBridgeHandler` and sets it as
the bridge handler for the Log4j 2.x stack, replacing the existing
JUL to SLF4J bridge that was used previously.

See gh-30003

spring-boot-project/spring-boot-starters/spring-boot-starter-log4j2/build.gradle

@@ -8,5 +8,4 @@ dependencies {
 	api("org.apache.logging.log4j:log4j-slf4j-impl")
 	api("org.apache.logging.log4j:log4j-core")
 	api("org.apache.logging.log4j:log4j-jul")
-	api("org.slf4j:jul-to-slf4j")
 }