Restore getUseRelativeRedirects in deprecated form

Restore the `getUseRelativeRedirects` method with a `Boolean` object
result and introduce `isUseRelativeRedirects` for the primitive boolean
variant.

See gh-20796

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java

@@ -537,7 +537,12 @@ public class ServerProperties {
 			this.redirectContextRoot = redirectContextRoot;
 		}
 
-		public boolean getUseRelativeRedirects() {
+		@Deprecated
+		public Boolean getUseRelativeRedirects() {
+			return this.useRelativeRedirects;
+		}
+
+		public boolean isUseRelativeRedirects() {
 			return this.useRelativeRedirects;
 		}
 

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/TomcatServletWebServerFactoryCustomizer.java

@@ -54,7 +54,7 @@ public class TomcatServletWebServerFactoryCustomizer
 		if (tomcatProperties.getRedirectContextRoot() != null) {
 			customizeRedirectContextRoot(factory, tomcatProperties.getRedirectContextRoot());
 		}
-		customizeUseRelativeRedirects(factory, tomcatProperties.getUseRelativeRedirects());
+		customizeUseRelativeRedirects(factory, tomcatProperties.isUseRelativeRedirects());
 		factory.setDisableMBeanRegistry(!tomcatProperties.getMbeanregistry().isEnabled());
 	}