Add lib.compilerConfig for GHC 9.6.x core libraries
Export a library function that downstream package sets can use to disable all GHC-bundled core libraries for GHC 9.6.x.
This provides a single source of truth for which libraries are bundled with this GHC version, making it easier for downstream package sets like horizon-build-packages and horizon-core to reuse the configuration.
Usage in downstream package sets:
compilerConfig = inputs.horizon-ghc.lib.compilerConfig;
Benefits:
- Single source of truth - GHC branch knows what it bundles
- No duplication of library lists across package sets
- Version-specific - each LTS branch has the correct list
- Simpler maintenance