Annotate null-checked method parameters with @Nullable

Add @Nullable to parameters of public methods that are explicitly checked for null. By default org.jspecify.annotations.Nullable is used, but through the nullableAnnotationClass option a custom annotation can be provided. Both @Target(TYPE_USE) and declaration annotations (e.g. javax.annotation.CheckForNull) are supported. Parameters that already carry a known nullable annotation are skipped to avoid duplication. This recipe scans for methods that do not already have parameters annotated with a nullable annotation and checks their usages for potential null checks. Additional null-checking methods can be specified via the additionalNullCheckingMethods option.