Add convenient api to java path customisation

Author: Mr3zee

gradle-plugin/api/gradle-plugin.api

@@ -160,6 +160,10 @@ public final class kotlinx/rpc/proto/ConstsKt {
 	public static final field PROTO_SOURCE_SETS Ljava/lang/String;
 }
 
+public final class kotlinx/rpc/proto/KxrpcPluginJarKt {
+	public static final fun getKxrpcProtocPluginJarPath (Lorg/gradle/api/Project;)Lorg/gradle/api/provider/Provider;
+}
+
 public abstract class kotlinx/rpc/proto/ProcessProtoFiles : org/gradle/api/tasks/Copy {
 	public fun <init> ()V
 }

gradle-plugin/src/main/kotlin/kotlinx/rpc/grpc/DefaultGrpcExtension.kt

@@ -256,7 +256,7 @@ internal open class DefaultGrpcExtension @Inject constructor(
     private fun createDefaultProtocPlugins() {
         protocPlugins.create(KXRPC) {
             local {
-                javaJar(project.configurations.named(KXRPC_PLUGIN_JAR_CONFIGURATION).map { it.singleFile.absolutePath })
+                javaJar(project.kxrpcProtocPluginJarPath)
             }
 
             options.put("debugOutput", "protobuf-kxrpc-plugin.log")

gradle-plugin/src/main/kotlin/kotlinx/rpc/proto/kxrpcPluginJar.kt

@@ -6,6 +6,22 @@ package kotlinx.rpc.proto
 
 import kotlinx.rpc.LIBRARY_VERSION
 import org.gradle.api.Project
+import org.gradle.api.provider.Provider
+
+/**
+ * Absolute path to the `kotlinx-rpc-protobuf-plugin` jar.
+ *
+ * Can be used to customise the java executable path:
+ * ```kotlin
+ * rpc.grpc.protocPlugins.kxrpc {
+ *     local {
+ *         javaJar(kxrpcProtocPluginJarPath, provider { "my-path-to-java" })
+ *     }
+ * }
+ * ```
+ */
+public val Project.kxrpcProtocPluginJarPath: Provider<String>
+    get() = project.configurations.named(KXRPC_PLUGIN_JAR_CONFIGURATION).map { it.singleFile.absolutePath }
 
 internal fun Project.configureKxRpcPluginJarConfiguration() {
     configurations.create(KXRPC_PLUGIN_JAR_CONFIGURATION)