Allow WebApplicationType to be deduced in a native image

Closes gh-31217

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/WebApplicationType.java

@@ -16,6 +16,9 @@
 
 package org.springframework.boot;
 
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.RuntimeHintsRegistrar;
+import org.springframework.aot.hint.TypeReference;
 import org.springframework.util.ClassUtils;
 
 /**
@@ -65,4 +68,24 @@ public enum WebApplicationType {
 		return WebApplicationType.SERVLET;
 	}
 
+	static class WebApplicationTypeRuntimeHintsRegistrar implements RuntimeHintsRegistrar {
+
+		@Override
+		public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+			for (String servletIndicatorClass : SERVLET_INDICATOR_CLASSES) {
+				registerTypeIfPresent(servletIndicatorClass, classLoader, hints);
+			}
+			registerTypeIfPresent(WEBFLUX_INDICATOR_CLASS, classLoader, hints);
+			registerTypeIfPresent(WEBMVC_INDICATOR_CLASS, classLoader, hints);
+		}
+
+		private void registerTypeIfPresent(String typeName, ClassLoader classLoader, RuntimeHints hints) {
+			if (ClassUtils.isPresent(typeName, classLoader)) {
+				hints.reflection().registerType(TypeReference.of(typeName), (hint) -> {
+				});
+			}
+		}
+
+	}
+
 }

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

@@ -1,4 +1,5 @@
 org.springframework.aot.hint.RuntimeHintsRegistrar=\
-org.springframework.boot.logging.logback.LogbackRuntimeHintsRegistrar
+org.springframework.boot.logging.logback.LogbackRuntimeHintsRegistrar,\
+org.springframework.boot.WebApplicationType.WebApplicationTypeRuntimeHintsRegistrar
 org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor=\
 org.springframework.boot.context.properties.ConfigurationPropertiesBeanFactoryInitializationAotProcessor