Add generated sources to delombok sourcepath

fixes #1301

Author: larsgrefer

lombok-plugin/src/main/java/io/freefair/gradle/plugins/lombok/LombokPlugin.java

@@ -101,9 +101,10 @@ private void configureSourceSetDefaults(SourceSet sourceSet) {
             handleLombokConfig(sourceSet, compileTaskProvider, delombokTaskProvider);
 
             delombokTaskProvider.configure(delombok -> {
-                delombok.getEncoding().set(compileTaskProvider.get().getOptions().getEncoding());
+                delombok.getEncoding().set(compileTaskProvider.map(c -> c.getOptions().getEncoding()));
                 delombok.getClasspath().from(sourceSet.getCompileClasspath());
                 delombok.getInput().from(sourceSet.getJava().getSourceDirectories());
+                delombok.getSourcepath().from(compileTaskProvider.flatMap(c -> c.getOptions().getGeneratedSourceOutputDirectory()));
                 delombok.dependsOn(sourceSet.getJava().getBuildDependencies());
             });
         });