Support for cross-repo code navigation

[varungandhi-src]

This should mostly "just work" with SCIP, but we haven't tested packages yet. We should fix this after completing:

• 1

• 30

High-level breakdown of the work involved here:

• [x] Support manually specifying file to gem mappings. https://github.com/sourcegraph/scip-ruby/pull/149
• [x] Support inferring file to gem mappings from standard Sorbet filesystem layout. https://github.com/sourcegraph/scip-ruby/pull/155
• [ ] https://github.com/sourcegraph/scip-ruby/pull/158
• [ ] Support inferring file to gem mappings from standard Bundler paths (for projects not using Sorbet).
• [x] 🐛 https://github.com/sourcegraph/scip-ruby/issues/157
• [ ] Emit external symbols in external_symbols list (not 100% sure if this is needed)
• [ ] Specially add Core and Standard APIs to Sourcegraph.
• [ ] Additional manual testing against Sourcegraph + refinement.

[varungandhi-src]

Related:

• https://github.com/sourcegraph/sourcegraph/issues/44122