Add serialization hint for ProblemDetail

Prior to this commit, a Spring web application would not be able to
serialize a `ProblemDetail` object instance in a Native Image, as
serialization hints would be missing.

This commit adds a RuntimeHints registrar that processes the
`ProblemDetail` type accordingly during the AOT phase.

Fixes gh-29801

spring-web/src/main/resources/META-INF/spring/aot.factories

@@ -2,6 +2,7 @@ org.springframework.aot.hint.RuntimeHintsRegistrar= \
 org.springframework.http.HttpMimeTypesRuntimeHints,\
 org.springframework.http.codec.CodecConfigurerRuntimeHints,\
 org.springframework.http.converter.json.JacksonModulesRuntimeHints,\
+org.springframework.http.converter.json.ProblemDetailRuntimeHints,\
 org.springframework.web.util.WebUtilRuntimeHints
 
 org.springframework.beans.factory.aot.BeanRegistrationAotProcessor=\