[GR-65850] [GR-68595] Fixing registration methods bypassing reachability handler creation and adding validation checks on registration methods.

[graalvmbot]

This PR resolves issues with some registration methods not creating reachability-handlers. Bypassing the reachability handler in conditional registrations immediately adds condition types to the image heap, which causes types to be treated as reachable even if they shouldn't be. By preventing this, we avoid increasing image size and ensure that the intended semantics of typeReachable conditions are preserved.
All proxy registrations should avoid directly calling com.oracle.svm.core.reflect.proxy.DynamicProxySupport#addProxyClass, and instead should call the new method com.oracle.svm.hosted.reflect.proxy.ProxyRegistry#registerProxy which creates reachability-handler for previous method.

Additionally, this update adds missing validation checks, such as null argument and registration phase validation, across registration methods to improve code reliability. Redundant code in subclasses of ConditionalConfigurationRegistry has been refactored for greater consistency and maintainability.