Make sure ProjectDescriptionDiff is created eagerly

This commit makes sure that the diff instance is created immediately,
taking a snapshot of the ProjectDescription before the customizers are
applied on it.

Previously, the instance was created as part of the supplier and
therefore created only once a component was requiring it.

See gh-1023

initializr-generator/src/main/java/io/spring/initializr/generator/project/ProjectGenerator.java

@@ -123,7 +123,10 @@ private Supplier<ProjectDescription> resolve(ProjectDescription description, Pro
 				MutableProjectDescription mutableDescription = (MutableProjectDescription) description;
 				ProjectDescriptionDiffFactory diffFactory = context.getBeanProvider(ProjectDescriptionDiffFactory.class)
 						.getIfAvailable(DefaultProjectDescriptionDiffFactory::new);
-				context.registerBean(ProjectDescriptionDiff.class, () -> diffFactory.create(mutableDescription));
+				// Create the diff here so that it takes a copy of the description
+				// immediately
+				ProjectDescriptionDiff diff = diffFactory.create(mutableDescription);
+				context.registerBean(ProjectDescriptionDiff.class, () -> diff);
 				context.getBeanProvider(ProjectDescriptionCustomizer.class).orderedStream()
 						.forEach((customizer) -> customizer.customize(mutableDescription));
 			}