Update WebFlux starter to depend on validation starter

Previously, the WebFlux starter declared direct dependencies on Hibernate Validator
and the Jakarta EE validation API. This meant that it required two exclusions to
exclude validation from a reactive web application that did not need it.

This commit updates the WebFlux starter to get its validation dependencies via a
dependency on the validation starter. This allows validation to be excluded
using a single exclusion. The EL dependency from the validation starter has
been excluded to allow the EL implementation from the underlying container
starter to continue to be used instead.

See gh-16593

spring-boot-project/spring-boot-starters/spring-boot-starter-webflux/pom.xml

@@ -28,16 +28,12 @@
 			<artifactId>spring-boot-starter-reactor-netty</artifactId>
 		</dependency>
 		<dependency>
-			<groupId>jakarta.validation</groupId>
-			<artifactId>jakarta.validation-api</artifactId>
-		</dependency>
-		<dependency>
-			<groupId>org.hibernate.validator</groupId>
-			<artifactId>hibernate-validator</artifactId>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-validation</artifactId>
 			<exclusions>
 				<exclusion>
-					<groupId>javax.validation</groupId>
-					<artifactId>validation-api</artifactId>
+					<groupId>org.apache.tomcat.embed</groupId>
+					<artifactId>tomcat-embed-el</artifactId>
 				</exclusion>
 			</exclusions>
 		</dependency>