Make devtools set spring.messages.reloadable=true

Update `DevToolsPropertyDefaultsPostProcessor` to automatically set
the recently introduced `spring.messages.reloadable` property to
`true`.

Closes spring-projectsgh-14699

Author: philwebb

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/env/DevToolsPropertyDefaultsPostProcessor.java

@@ -73,6 +73,7 @@ public class DevToolsPropertyDefaultsPostProcessor implements EnvironmentPostPro
 		properties.put("server.error.include-stacktrace", "ALWAYS");
 		properties.put("server.servlet.jsp.init-parameters.development", "true");
 		properties.put("spring.reactor.stacktrace-mode.enabled", "true");
+		properties.put("spring.messages.reloadable", "true");
 		PROPERTIES = Collections.unmodifiableMap(properties);
 	}
 

spring-boot-project/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/env/DevToolPropertiesIntegrationTests.java

@@ -114,6 +114,17 @@ public void postProcessEnablesIncludeStackTraceProperty() {
 				.isEqualTo(ErrorProperties.IncludeStacktrace.ALWAYS.toString());
 	}
 
+	@Test
+	public void postProcessEnablesMessageSourceReloadProperty() {
+		SpringApplication application = new SpringApplication(TestConfiguration.class);
+		application.setWebApplicationType(WebApplicationType.NONE);
+		this.context = application.run();
+		ConfigurableEnvironment environment = this.context.getEnvironment();
+		Boolean property = environment.getProperty("spring.messages.reloadable",
+				Boolean.class);
+		assertThat(property).isTrue();
+	}
+
 	@Configuration
 	static class TestConfiguration {