Migrate to the `reachability-metadata.json` format and release 1.0.0

[vjovanov]

Summary

We are migrating to the new, more concise metadata format. This move is essential to support GraalVM 25, which provides critical fixes for the native-image agent and improves metadata precision.

Key Drivers & Benefits

This migration provides two main advantages:

1. Format Efficiency: The new format is more concise and reduces the number of required entries.
2. GraalVM 25 Support: This is the primary driver. Upgrading allows us to leverage:
   • Fixes for numerous native-image agent issues.
   • The new native agent, which significantly improves the precision of the required metadata.

Implementation Plan

The migration will be executed as follows:

1. The repository will be bumped to version 1.0.0, which will include the reachability-metadata-schema.json file in the release.
2. The previous metadata version will be maintained on a 0.3.x branch to support any potential future legacy releases.

The native build tools will dispatch to the metadata release in the following way:

1. GraalVM distribution include the reachability-metadata-schema.json higher than the repo => use the latest repo version
2. GraalVM distribution has the reachability-metadata-schema.json lower than the repo => exit and warn about updating
3. GraalVM distribution has no reachability-metadata-schema.json => use version 0.3.x

Necessary fixes before the 1.0.0 release:

• Remove index.json from the project root and from the individual test folders #4

From the Discussion with the Community

1. Do we want a special case for 25.0.0 and 25.0.1 that don't have reachability-metadata-schema.json? No, no need to rush.
2. Do we want to keep the forking mechanism for the future? Not for now. We can treat this as a separate request.