Allow plugins to use SLF4J for logging

SLF4J is a commonly used abstraction for various logging frameworks
such as java.util.logging (JUL) or Log4j. Currently, plugins are
required to do all their logging using the provided JUL logger.
This is annoying for plugins that target multiple platforms or when
using libraries that log messages using SLF4J.

Expose SLF4J as optional logging API for plugins, so they can use
it without having to shade it in the plugin and going through
several layers of logging abstraction.

paper-api/build.gradle.kts

@@ -12,6 +12,8 @@ java {
 val annotationsVersion = "24.1.0"
 val bungeeCordChatVersion = "1.20-R0.2"
 val adventureVersion = "4.17.0"
+val slf4jVersion = "2.0.9"
+val log4jVersion = "2.17.1"
 val apiAndDocs: Configuration by configurations.creating {
     attributes {
         attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category.DOCUMENTATION))
@@ -61,6 +63,8 @@ dependencies {
     apiAndDocs("net.kyori:adventure-text-serializer-legacy")
     apiAndDocs("net.kyori:adventure-text-serializer-plain")
     apiAndDocs("net.kyori:adventure-text-logger-slf4j")
+    api("org.apache.logging.log4j:log4j-api:$log4jVersion")
+    api("org.slf4j:slf4j-api:$slf4jVersion")
 
     implementation("org.ow2.asm:asm:9.7.1")
     implementation("org.ow2.asm:asm-commons:9.7.1")
@@ -155,6 +159,8 @@ tasks.withType<Javadoc> {
         "https://jd.advntr.dev/text-serializer-legacy/$adventureVersion/",
         "https://jd.advntr.dev/text-serializer-plain/$adventureVersion/",
         "https://jd.advntr.dev/text-logger-slf4j/$adventureVersion/",
+        "https://javadoc.io/doc/org.slf4j/slf4j-api/$slf4jVersion/",
+        "https://javadoc.io/doc/org.apache.logging.log4j/log4j-api/$log4jVersion/",
         // Paper end
         "https://javadoc.io/doc/org.apache.maven.resolver/maven-resolver-api/1.7.3", // Paper
     )

paper-api/src/main/java/org/bukkit/plugin/Plugin.java

@@ -198,6 +198,22 @@ public interface Plugin extends TabExecutor {
     }
     // Paper end
 
+    // Paper start - Add SLF4J/Log4J loggers
+    @NotNull
+    default org.slf4j.Logger getSLF4JLogger() {
+        return org.slf4j.LoggerFactory.getLogger(getLogger().getName());
+    }
+
+    /**
+     * @deprecated use {@link #getSLF4JLogger()}
+     */
+    @Deprecated
+    @NotNull
+    default org.apache.logging.log4j.Logger getLog4JLogger() {
+        return org.apache.logging.log4j.LogManager.getLogger(getLogger().getName());
+    }
+    // Paper end
+
     /**
      * Returns the name of the plugin.
      * <p>