Language Service: Move ReferencesProvider out of the language server

[marcoroth]

This pull request moves the last of the providers into @herb-tools/language-service.

ReferencesProvider stayed behind in #2162 because it dependent on things that couldn't be offered by the package yet. #2168 and ProjectIndex removed most of that, and what was left came down to three small dependencies.

Project was used for this.project.root, twice. ProjectIndex already exposes root, so the dependency disappears rather than moving.

Documents was used for one call, this.documents.get(uri), to prefer an open buffer over what is on disk. That is a two line interface, so the provider no longer reaches into the language server's document store:

node:fs and node:path follow the pattern the other moved providers already use. readFileSync becomes a required injected read, matching DefinitionProvider, and join comes from the package's own posix_path.

The read closure is now built once in Session and shared through SharedServices.

[github-actions]

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_{🌱 Grown from commit 60dd24d}

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✅ Preview deployment has been cleaned up.

[pkg-pr-new]

npx https://pkg.pr.new/@herb-tools/formatter@2186

npx https://pkg.pr.new/@herb-tools/language-server@2186

npx https://pkg.pr.new/@herb-tools/linter@2186

commit: 60dd24d