Add simple utility method for defining an entrypoint with a language adapter (#1451)

src/main/java/net/fabricmc/loom/api/fmj/FabricModJsonV1Spec.java

@@ -122,6 +122,19 @@ public abstract class FabricModJsonV1Spec {
 		entrypoint(entrypoint, value, metadata -> { });
 	}
 
+	/**
+	 * Add a new entrypoint with the given name, value, and language adapter.
+	 *
+	 * @param entrypoint The name of the entrypoint, such as "main" or "client"
+	 * @param value The value of the entrypoint, typically a fully qualified class name
+	 * @param adapter The language adapter of the entrypoint, such as "kotlin" or "scala"
+	 */
+	public void entrypoint(String entrypoint, String value, String adapter) {
+		entrypoint(entrypoint, value, metadata -> {
+			metadata.getAdapter().set(adapter);
+		});
+	}
+
 	/**
 	 * Add a new entrypoint with the given name and value, and configure it with the given action.
 	 *

src/test/groovy/net/fabricmc/loom/test/unit/fmj/FabricModJsonV1GeneratorTest.groovy

@@ -303,6 +303,7 @@ class FabricModJsonV1GeneratorTest extends Specification {
 		spec.entrypoint("client", "com.example.KotlinClient::init") {
 			it.adapter.set("kotlin")
 		}
+		spec.entrypoint("client", "com.example.KotlinClient", "kotlin")
 		spec.entrypoint("client") {
 			it.value.set("com.example.Client")
 		}
@@ -322,6 +323,10 @@ class FabricModJsonV1GeneratorTest extends Specification {
 		        "value": "com.example.KotlinClient::init",
 		        "adapter": "kotlin"
 		      },
+		      {
+		        "value": "com.example.KotlinClient",
+		        "adapter": "kotlin"
+		      },
 		      "com.example.Client"
 		    ],
 		    "main": [