Rationalize hints required for annotations

This commit updates RuntimeHintsUtils to focus on registering a JDK
proxy only as annotations of annotated elements that have at least
an introspection hints are visible out-of-the-box.

This commit also removes unnecessary hints and adapt `@Reflective` to
detect if a hint is required using the introduced
MergedAnnotation#isSynthesizable.

See gh-28967

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

@@ -1,3 +1,2 @@
 org.springframework.aot.hint.RuntimeHintsRegistrar=\
-org.springframework.aot.hint.support.CoreAnnotationsRuntimeHints,\
 org.springframework.aot.hint.support.SpringFactoriesLoaderRuntimeHints