Refine auto-configurations conditions

Prior to this commit, auto-configurations were only checking for the
presence of GraphQL Java classes as guards, assuming that Spring
GraphQL classes were always on the classpath.

Auto-configurations are meant to be moved to the Spring Boot project in
the future, so this commit adds the relevant condition class checks to
reflect that spring-graphql might not be on the classpath.

graphql-spring-boot-starter/src/main/java/org/springframework/graphql/boot/GraphQlAutoConfiguration.java

@@ -46,7 +46,7 @@ import org.springframework.graphql.execution.GraphQlSource;
  * @since 1.0.0
  */
 @Configuration(proxyBeanMethods = false)
-@ConditionalOnClass(GraphQL.class)
+@ConditionalOnClass({GraphQL.class, GraphQlSource.class})
 @ConditionalOnMissingBean(GraphQlSource.class)
 @EnableConfigurationProperties(GraphQlProperties.class)
 public class GraphQlAutoConfiguration {

graphql-spring-boot-starter/src/main/java/org/springframework/graphql/boot/GraphQlServiceAutoConfiguration.java

@@ -36,7 +36,7 @@ import org.springframework.graphql.execution.GraphQlSource;
  * @since 1.0.0
  */
 @Configuration(proxyBeanMethods = false)
-@ConditionalOnClass(GraphQL.class)
+@ConditionalOnClass({GraphQL.class, GraphQlService.class})
 @ConditionalOnMissingBean(GraphQlService.class)
 @AutoConfigureAfter(GraphQlAutoConfiguration.class)
 public class GraphQlServiceAutoConfiguration {

graphql-spring-boot-starter/src/main/java/org/springframework/graphql/boot/GraphQlWebFluxAutoConfiguration.java

@@ -66,7 +66,7 @@ import static org.springframework.web.reactive.function.server.RequestPredicates
  */
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.REACTIVE)
-@ConditionalOnClass(GraphQL.class)
+@ConditionalOnClass({GraphQL.class, GraphQlHttpHandler.class})
 @ConditionalOnBean(GraphQlSource.class)
 @AutoConfigureAfter(GraphQlServiceAutoConfiguration.class)
 public class GraphQlWebFluxAutoConfiguration {

graphql-spring-boot-starter/src/main/java/org/springframework/graphql/boot/GraphQlWebMvcAutoConfiguration.java

@@ -73,7 +73,7 @@ import static org.springframework.web.servlet.function.RequestPredicates.content
  */
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
-@ConditionalOnClass(GraphQL.class)
+@ConditionalOnClass({GraphQL.class, GraphQlHttpHandler.class})
 @ConditionalOnBean(GraphQlSource.class)
 @AutoConfigureAfter(GraphQlServiceAutoConfiguration.class)
 public class GraphQlWebMvcAutoConfiguration {