JENKINS-75019 - Use uber classloader on built-in node

Make sure that we are using the uber classloader from the plugin manager
when we're running on the built-in node. This is done by ensuring that
the `ControllerGroovyScript` class is used for running scripts when
we're running on the built-in node, which sets the right classloader.

Author: mtughan

src/main/java/org/jenkinsci/plugins/scriptler/builder/ScriptlerBuilder.java

@@ -11,13 +11,7 @@
 import hudson.ExtensionList;
 import hudson.FilePath;
 import hudson.Launcher;
-import hudson.model.AbstractBuild;
-import hudson.model.AbstractProject;
-import hudson.model.BuildListener;
-import hudson.model.Failure;
-import hudson.model.ParameterValue;
-import hudson.model.ParametersAction;
-import hudson.model.Project;
+import hudson.model.*;
 import hudson.remoting.VirtualChannel;
 import hudson.security.Permission;
 import hudson.tasks.BuildStepDescriptor;
@@ -261,7 +255,7 @@ public boolean perform(AbstractBuild<?, ?> build, Launcher launcher, BuildListen
                         parameter.getName(), TokenMacro.expandAll(build, listener, parameter.getValue())));
             }
             final Object output;
-            if (script.onlyBuiltIn) {
+            if (script.onlyBuiltIn || Computer.currentComputer() instanceof Jenkins.MasterComputer) {
                 // When run on the built-in node, make build, launcher, listener available to script
                 output = FilePath.localChannel.call(new ControllerGroovyScript(
                         script.getScriptText(), expandedParams, true, listener, launcher, build));

src/main/java/org/jenkinsci/plugins/scriptler/util/ScriptHelper.java

@@ -171,8 +171,14 @@ public static String runScript(String node, String scriptTxt, @NonNull Collectio
             try {
                 Computer comp = Jenkins.get().getComputer(node);
                 TaskListener listener = new StreamTaskListener(sos, StandardCharsets.UTF_8);
-                if (comp == null && NodeNames.BUILT_IN.equals(node)) {
-                    FilePath.localChannel.call(new GroovyScript(scriptTxt, parameters, false, listener));
+                if (NodeNames.BUILT_IN.equals(node)) {
+                    FilePath.localChannel.call(new ControllerGroovyScript(
+                            scriptTxt,
+                            parameters,
+                            false,
+                            listener,
+                            Jenkins.get().createLauncher(listener),
+                            null));
                 } else if (comp != null && comp.getChannel() != null) {
                     comp.getChannel().call(new GroovyScript(scriptTxt, parameters, false, listener));
                 }