Fix log4j package warning on JMeter startup: WARN StatusConsoleListener The use of package scanning to locate plugins is deprecated ...

The Log4j Core `packages` configuration attribute is deprecated because:

* It triggers the scanning of the mentioned packages and slows down the
  startup process.
* It was replaced in version 2.0 by a faster mechanism that relies on a
  `Log4jPlugins.dat` metadata file. See [Log4j Plugins](https://logging.apache.org/log4j/2.x/manual/plugins.html) for more details.

This PR removes the `packages` attribute from the standard configuration
file and configures the build script of `jmeter-core` to use the
`PluginProcessor` contained in `log4j-core`.

See #5937.

Author: ppkarwasz

bin/log4j2.xml

@@ -16,7 +16,7 @@
   ~ limitations under the License.
   -->
 
-<Configuration status="WARN" packages="org.apache.jmeter.gui.logging">
+<Configuration status="WARN">
 
   <Appenders>
     <!-- Uncomment to set rotating logs up to 5 files of 100 MB-->

src/core/build.gradle.kts

@@ -17,6 +17,7 @@
 
 import com.github.autostyle.gradle.AutostyleTask
 import com.github.vlsi.gradle.ide.IdeExtension
+import java.util.jar.JarFile
 
 plugins {
     id("java-test-fixtures")
@@ -45,6 +46,9 @@ dependencies {
     api("org.apache.logging.log4j:log4j-core") {
         because("GuiLogEventAppender is using log4j-core to implement GUI-based log appender")
     }
+    kapt("org.apache.logging.log4j:log4j-core") {
+        because("Generates a plugin cache file for GuiLogEventAppender")
+    }
     api("org.apache.logging.log4j:log4j-slf4j-impl") {
         because("Both log4j and slf4j are included, so it makes sense to just add log4j->slf4j bridge as well")
     }
@@ -188,3 +192,16 @@ tasks.jar {
         from("$rootDir/xdocs/images/logo.svg")
     }
 }
+
+// Checks the generated JAR for a Log4j plugin cache file.
+tasks.jar {
+    doLast {
+        val jarFile = archiveFile.get().asFile
+        JarFile(jarFile).use { jar ->
+            val entryName = "META-INF/org/apache/logging/log4j/core/config/plugins/Log4j2Plugins.dat"
+            if (jar.getJarEntry(entryName) == null) {
+                throw IllegalStateException("$entryName was not found in $jarFile. The entry should be generated by log4j-core annotation processor")
+            }
+        }
+    }
+}