Automatically ignore mapping roots shared by build time and runtime

[radcortez]

Description

In extensions, when a mapping root shares the same prefix between build time and runtime, it can cause a [property] does not map to any root error. It happens when a configuration value meant to be built-time or runtime-only is available in a shared config source (like application.properties).

For the quarkus namespace we ignore the SmallRye Config behaviour with https://github.com/quarkusio/quarkus/blob/main/core/runtime/src/main/java/io/quarkus/runtime/configuration/QuarkusConfigBuilderCustomizer.java#L138

Extensions that use different namespaces have to ignore this manually.

See #47664

Implementation ideas

We should be able to detect such cases and automatically ignore them without requiring additional code from the extension side.