feat: add 1.21.5 support

v1_21_R4/build.gradle.kts

@@ -0,0 +1,30 @@
+plugins {
+    id("java")
+    id("io.papermc.paperweight.userdev")
+}
+
+dependencies {
+    paperweight.paperDevBundle("1.21.5-R0.1-SNAPSHOT")
+    implementation(project(":common"))
+}
+
+tasks {
+
+    build {
+        dependsOn(reobfJar)
+    }
+
+    compileJava {
+        options.encoding = Charsets.UTF_8.name()
+    }
+    java {
+        toolchain.languageVersion.set(JavaLanguageVersion.of(21));
+    }
+
+    javadoc {
+        options.encoding = Charsets.UTF_8.name()
+    }
+    processResources {
+        filteringCharset = Charsets.UTF_8.name()
+    }
+}