Add HttpEncodingAutoConfiguration to WebMvcTest

Prior to this commit, tests using the `@WebMvcTest` annotation would not
include the `HttpEncodingAutoConfiguration`. This means that, even if
configured, the encoding filter would not be configured in MVC tests,
resulting in an inconsistency with `@SpringBootTest` tests.

This commit ensures that the `HttpEncodingAutoConfiguration` is included
when `@WebMvcTest` is used.

Fixes gh-23749

spring-boot-project/spring-boot-test-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -152,6 +152,7 @@ org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
 org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
 org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
 org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
+org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
 org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration
 
 # DefaultTestExecutionListenersPostProcessors

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/servlet/WebMvcTestAutoConfigurationIntegrationTests.java

@@ -24,6 +24,7 @@ import org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAuto
 import org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration;
 import org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration;
 import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration;
 import org.springframework.context.ApplicationContext;
 import org.springframework.core.task.AsyncTaskExecutor;
 import org.springframework.test.util.ReflectionTestUtils;
@@ -76,4 +77,9 @@ class WebMvcTestAutoConfigurationIntegrationTests {
 				"taskExecutor")).isSameAs(this.applicationContext.getBean("applicationTaskExecutor"));
 	}
 
+	@Test
+	void httpEncodingAutoConfigurationWasImported() {
+		assertThat(this.applicationContext).has(importedAutoConfiguration(HttpEncodingAutoConfiguration.class));
+	}
+
 }