@Override
    public Builder toBuilder() {
        Builder builder = builder()
                .model(model)
                .events(events)
                .settings(settings)
                .fileManifest(fileManifest)
                .pluginClassLoader(pluginClassLoader)
                .sources(sources)
                .artifactName(artifactName);
        getProjection().ifPresent(config -> builder.projection(projectionName, config));
        getOriginalModel().ifPresent(builder::originalModel);
        return builder;
    }
Checks if the given metadata key-value pair is either not present
in the old model (thus a new, source metadata), or is present and
the filename of the entry in the original model matches one of
the defined {@code sources}.

@param metadataKey Metadata key to check.
@return Returns true if this metadata is considered a source entry.
smithy-build/src/main/java/software/amazon/smithy/build/PluginContext.java