Use @SafeVarargs in Jackson builder and factory

Using @SafeVarargs in Jackson mapper builder and factory bean classes
allows the varargs methods to be used without a compiler warning. The
implementations of these methods do not perform unsafe operations on
their varargs parameter. It is therefore safe to add this annotation.

The following two methods are changed:

- add @SafeVarargs to Jackson2ObjectMapperBuilder#modulesToInstall
  and make it final
- add @SafeVarargs to
  Jackson2ObjectMapperFactoryBean#setModulesToInstall and make it final

This is a backwards incompatible change as these methods now have to be
declared final. Existing subclasses that override one of these methods
will break.

Closes gh-25311

spring-web/src/main/java/org/springframework/http/converter/json/Jackson2ObjectMapperBuilder.java

@@ -595,8 +595,8 @@ public class Jackson2ObjectMapperBuilder {
 	 * @see #modulesToInstall(Module...)
 	 * @see com.fasterxml.jackson.databind.Module
 	 */
-	@SuppressWarnings("unchecked")
-	public Jackson2ObjectMapperBuilder modulesToInstall(Class<? extends Module>... modules) {
+	@SafeVarargs
+	public final Jackson2ObjectMapperBuilder modulesToInstall(Class<? extends Module>... modules) {
 		this.moduleClasses = modules;
 		this.findWellKnownModules = true;
 		return this;

spring-web/src/main/java/org/springframework/http/converter/json/Jackson2ObjectMapperFactoryBean.java

@@ -409,8 +409,8 @@ public class Jackson2ObjectMapperFactoryBean implements FactoryBean<ObjectMapper
 	 * @since 4.0.1
 	 * @see com.fasterxml.jackson.databind.Module
 	 */
-	@SuppressWarnings("unchecked")
-	public void setModulesToInstall(Class<? extends Module>... modules) {
+	@SafeVarargs
+	public final void setModulesToInstall(Class<? extends Module>... modules) {
 		this.builder.modulesToInstall(modules);
 	}