[8.7.0] Cherry-pick remote repo contents cache feature

[fmeum]

Summary

Cherry-picks the remote repo contents cache feature from master to release-8.7.0.

This consists of:

• 3 manual prerequisite ports (recorded input ordering, repo env handling, predeclaredInputHash/ImmutableSortedMap changes)
• 1 non-functional refactoring prerequisite
• 20 feature commits implementing the remote repo contents cache

The remote repo contents cache allows caching external repository contents in a remote cache (HTTP/gRPC), served via an in-memory overlay filesystem (RemoteExternalOverlayFileSystem). This builds on the local repo contents cache already present on release-8.7.0.

Prerequisite commits (manually ported)

• 5e3f0c8373 — Refactoring from: Make external repo file checking actually useful
• 41ccfefb88 — Preserve order of recorded inputs (ImmutableMap → ImmutableSortedMap, Comparable on subclasses)
• 01407ce758 — Fix and consolidate repo env handling (RepoEnvironmentFunction, EnvironmentVariableValue)
• fe040a3271 — Fold environ into the predeclared inputs hash

Feature commits (cherry-picked with -x)

1. Fix crash when repo contents cache is under the main repo
2. Deduplicate identical repo contents cache entries during GC
3. Make naming scheme for repo contents cache entries more reliable
4. Prepare for the addition of a remote repo contents cache
5. Add a remote repo contents cache
6. Reproduce a Skyframe cycle with the repo contents cache in a test
7. Fix NPE with remote repo contents cache
8. Make remote repo contents cache less spammy
9. Fix materialization edge cases in the remote repo contents cache
10. Fix RemoteExternalOverlayFileSystem#resolveSymbolicLinks
11. Allow more general exceptions in getConfiguration
12. Prefetch .bzl files in the remote repo contents cache
13. Show stack traces in the remote repo contents cache with --verbose_failures
14. Fix repo contents cache FileValue staleness
15. Get the local and remote repo contents cache to work together
16. Clarify the invalidation of REPO_CONTENTS_CACHE_DIRS FileStateValues
17. Fix cycles when checking the local repo contents cache
18. Fix remote repo contents cache issues
19. Materialize important outputs from remote external repos

Adaptation notes

Key structural differences from master:

• On release-8.7.0, RepositoryDelegatorFunction.java + StarlarkRepositoryFunction.java exist separately; on master they were merged into RepositoryFetchFunction.java
• DigestWriter is an inner class of RepositoryDelegatorFunction on release-8.7.0; it's a separate file on master
• RepoEnvironmentFunction on release-8.7.0 checks PrecomputedValue.REPO_ENV first, then falls back to ClientEnvironmentFunction (vs master's consolidated approach

Test plan

• passes
• Full CI

🤖 Generated with Claude Code

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com
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