Restore AlwaysVisible

[gmac]

Restores AlwaysVisible, which provides some schema performance benefits. This feature was previously removed for compatibility with GraphQL Ruby v2.5.3, which switched AlwaysVisible to use the new Visibility system.

This update makes supergraphs generally more compatible with Visibility:

• Composer generates a sealed schema with all supergraph directives.
• All schema changes and traversals happen before installing visibility.
• Supergraph is now always derived from schema directives, eliminating compose/rehydrate discrepancies.
• Tests avoid destructive changes to base GraphQL resources.

This further positions the stitching library to incorporate Visibility profiles for managing audience distributions.