fix: use URLClassLoader with ResourceProvider in Maven plugins

Fixes vaadin/hilla#2637

ResourceProvider ignored the actual project's resources when using the default ClassLoader. This resulted in loading `vaadin-featureflags.properties` from the vaadin-dev-bundle jar, even though there is a file in the project.

flow-plugins/flow-plugin-base/src/main/java/com/vaadin/flow/utils/LookupImpl.java

@@ -45,7 +45,7 @@ public LookupImpl(ClassFinder classFinder) {
  @Override
  public <T> T lookup(Class<T> serviceClass) {
  if (ResourceProvider.class.isAssignableFrom(serviceClass)) {
- return serviceClass.cast(new ResourceProviderImpl());
+ return serviceClass.cast(new ResourceProviderImpl(classFinder.getClassLoader()));
  }
  return lookupAll(serviceClass).stream().findFirst().orElse(null);
  }

flow-plugins/flow-plugin-base/src/main/java/com/vaadin/flow/utils/ResourceProviderImpl.java

@@ -18,6 +18,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.URL;
+import java.net.URLClassLoader;
 import java.util.Collections;
 import java.util.List;
 
@@ -31,6 +32,16 @@
  */
 class ResourceProviderImpl implements ResourceProvider {
 
+ private ClassLoader classLoader;
+
+ ResourceProviderImpl() {
+ this(ResourceProviderImpl.class.getClassLoader());
+ }
+
+ ResourceProviderImpl(ClassLoader classLoader) {
+ this.classLoader = classLoader;
+ }
+
  @Override
  public URL getApplicationResource(String path) {
  return ResourceProviderImpl.class.getClassLoader().getResource(path);