fix: apply java-library plugin to Grails Plugin projects

Grails plugins are Java libraries and should have access
to the `api` dependency configuration by default.

Author: matrei

grails-gradle/plugins/src/main/groovy/org/grails/gradle/plugin/core/GrailsPluginGradlePlugin.groovy

@@ -60,6 +60,8 @@ class GrailsPluginGradlePlugin extends GrailsGradlePlugin {
     void apply(Project project) {
         super.apply(project)
 
+        project.pluginManager.apply('java-library')
+
         checkForConfigurationClash(project)
 
         configureAstSources(project)